Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Doug Anderson]

Hi,

On Tue, Feb 27, 2018 at 5:38 PM, Karthikeyan Ramasubramanian
<kramasub@codeaurora.org> wrote:
> This bus driver supports the GENI based i2c hardware controller in the
> Qualcomm SOCs. The Qualcomm Generic Interface (GENI) is a programmable
> module supporting a wide range of serial interfaces including I2C. The
> driver supports FIFO mode and DMA mode of transfer and switches modes
> dynamically depending on the size of the transfer.
>
> Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
> Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
> Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>
> ---
>  drivers/i2c/busses/Kconfig         |  11 +
>  drivers/i2c/busses/Makefile        |   1 +
>  drivers/i2c/busses/i2c-qcom-geni.c | 626 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 638 insertions(+)

I'm not an expert on geni (and, to be honest, I haven't read the main
geni patch yet).  ...but I figured I could at least add my $0.02 since
I've stared at i2c bus drivers a lot in the past.  Feel free to tell
me if I'm full or crap...


>  create mode 100644 drivers/i2c/busses/i2c-qcom-geni.c
>
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index e2954fb..1ddf5cd 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -848,6 +848,17 @@ config I2C_PXA_SLAVE
>           is necessary for systems where the PXA may be a target on the
>           I2C bus.
>
> +config I2C_QCOM_GENI
> +       tristate "Qualcomm Technologies Inc.'s GENI based I2C controller"
> +       depends on ARCH_QCOM
> +       depends on QCOM_GENI_SE
> +       help
> +         If you say yes to this option, support will be included for the
> +         built-in I2C interface on the Qualcomm Technologies Inc.'s SoCs.

Kind of a generic description and this driver is only for new SoCs,
right?  Maybe make it a little more specific?


> +
> +         This driver can also be built as a module.  If so, the module
> +         will be called i2c-qcom-geni.
> +
>  config I2C_QUP
>         tristate "Qualcomm QUP based I2C controller"
>         depends on ARCH_QCOM
> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
> index 2ce8576..201fce1 100644
> --- a/drivers/i2c/busses/Makefile
> +++ b/drivers/i2c/busses/Makefile
> @@ -84,6 +84,7 @@ obj-$(CONFIG_I2C_PNX)         += i2c-pnx.o
>  obj-$(CONFIG_I2C_PUV3)         += i2c-puv3.o
>  obj-$(CONFIG_I2C_PXA)          += i2c-pxa.o
>  obj-$(CONFIG_I2C_PXA_PCI)      += i2c-pxa-pci.o
> +obj-$(CONFIG_I2C_QCOM_GENI)    += i2c-qcom-geni.o
>  obj-$(CONFIG_I2C_QUP)          += i2c-qup.o
>  obj-$(CONFIG_I2C_RIIC)         += i2c-riic.o
>  obj-$(CONFIG_I2C_RK3X)         += i2c-rk3x.o
> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> new file mode 100644
> index 0000000..e1e4268
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -0,0 +1,626 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2017-2018, The Linux Foundation. All rights reserved.
> +
> +#include <linux/clk.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/qcom-geni-se.h>
> +
> +#define SE_I2C_TX_TRANS_LEN            0x26c
> +#define SE_I2C_RX_TRANS_LEN            0x270
> +#define SE_I2C_SCL_COUNTERS            0x278
> +
> +#define SE_I2C_ERR  (M_CMD_OVERRUN_EN | M_ILLEGAL_CMD_EN | M_CMD_FAILURE_EN |\
> +                       M_GP_IRQ_1_EN | M_GP_IRQ_3_EN | M_GP_IRQ_4_EN)
> +#define SE_I2C_ABORT           BIT(1)
> +
> +/* M_CMD OP codes for I2C */
> +#define I2C_WRITE              0x1
> +#define I2C_READ               0x2
> +#define I2C_WRITE_READ         0x3
> +#define I2C_ADDR_ONLY          0x4
> +#define I2C_BUS_CLEAR          0x6
> +#define I2C_STOP_ON_BUS                0x7
> +/* M_CMD params for I2C */
> +#define PRE_CMD_DELAY          BIT(0)
> +#define TIMESTAMP_BEFORE       BIT(1)
> +#define STOP_STRETCH           BIT(2)
> +#define TIMESTAMP_AFTER                BIT(3)
> +#define POST_COMMAND_DELAY     BIT(4)
> +#define IGNORE_ADD_NACK                BIT(6)
> +#define READ_FINISHED_WITH_ACK BIT(7)
> +#define BYPASS_ADDR_PHASE      BIT(8)
> +#define SLV_ADDR_MSK           GENMASK(15, 9)
> +#define SLV_ADDR_SHFT          9
> +/* I2C SCL COUNTER fields */
> +#define HIGH_COUNTER_MSK       GENMASK(29, 20)
> +#define HIGH_COUNTER_SHFT      20
> +#define LOW_COUNTER_MSK                GENMASK(19, 10)
> +#define LOW_COUNTER_SHFT       10
> +#define CYCLE_COUNTER_MSK      GENMASK(9, 0)
> +
> +#define GP_IRQ0                        0
> +#define GP_IRQ1                        1
> +#define GP_IRQ2                        2
> +#define GP_IRQ3                        3
> +#define GP_IRQ4                        4
> +#define GP_IRQ5                        5
> +#define GENI_OVERRUN           6
> +#define GENI_ILLEGAL_CMD       7
> +#define GENI_ABORT_DONE                8
> +#define GENI_TIMEOUT           9

Above should be an enum; then use the enum type as the parameter to
geni_i2c_err() so it's obvious that "err" is not a normal linux error
code.


> +#define I2C_NACK               GP_IRQ1
> +#define I2C_BUS_PROTO          GP_IRQ3
> +#define I2C_ARB_LOST           GP_IRQ4

Get rid of definition of GP_IRQ1, 3, and 4 and just define I2C_NACK,
I2C_BUS_PROTO, and I2C_ARB_LOST directly.


> +#define DM_I2C_CB_ERR          ((BIT(GP_IRQ1) | BIT(GP_IRQ3) | BIT(GP_IRQ4)) \
> +                                                                       << 5)

Should these really be using "GP_IRQ1", "GP_IRQ3", and "GP_IRQ4".
Does this use of those numbers have anything to do with the other use
of them?  Seems like this should just be BIT(1) | BIT(3) | BIT(4).

Said another way: does bit 1 in this field coorespond to NACK, bit 3
correspond to BUS_PROTO, and bit 4 correspond to ARB_LOST?  If not
then I see no reason to try to tie them together.  If they do
correspond then use BIT(I2C_NACK), etc...


> +
> +#define I2C_AUTO_SUSPEND_DELAY 250

Why 250 ms?  That seems like an eternity.  Is it really that expensive
to turn resources off and on?  I would sorta just expect clocks and
stuff to get turned off right after a transaction finished unless
another one was pending right behind it...


> +#define KHz(freq)              (1000 * freq)

I probably wouldn't define KHz macro and just used numbers like 100000
like all the other i2c drivers, but I guess it's OK.  Should be all
caps, though?


> +#define PACKING_BYTES_PW       4
> +
> +struct geni_i2c_dev {
> +       struct geni_se se;
> +       u32 tx_wm;
> +       int irq;
> +       int err;
> +       struct i2c_adapter adap;
> +       struct completion done;
> +       struct i2c_msg *cur;
> +       int cur_wr;
> +       int cur_rd;
> +       u32 clk_freq_out;
> +       const struct geni_i2c_clk_fld *clk_fld;
> +};
> +
> +struct geni_i2c_err_log {
> +       int err;
> +       const char *msg;
> +};
> +
> +static struct geni_i2c_err_log gi2c_log[] = {

static const?


> +       [GP_IRQ0] = {-EINVAL, "Unknown I2C err GP_IRQ0"},
> +       [I2C_NACK] = {-ENOTCONN, "NACK: slv unresponsive, check its power/reset-ln"},

Longer than 80 characters; don't split the string, but you could still
wrap better.


> +       [GP_IRQ2] = {-EINVAL, "Unknown I2C err GP IRQ2"},
> +       [I2C_BUS_PROTO] = {-EPROTO, "Bus proto err, noisy/unepxected start/stop"},
> +       [I2C_ARB_LOST] = {-EBUSY, "Bus arbitration lost, clock line undriveable"},
> +       [GP_IRQ5] = {-EINVAL, "Unknown I2C err GP IRQ5"},
> +       [GENI_OVERRUN] = {-EIO, "Cmd overrun, check GENI cmd-state machine"},
> +       [GENI_ILLEGAL_CMD] = {-EILSEQ, "Illegal cmd, check GENI cmd-state machine"},
> +       [GENI_ABORT_DONE] = {-ETIMEDOUT, "Abort after timeout successful"},
> +       [GENI_TIMEOUT] = {-ETIMEDOUT, "I2C TXN timed out"},
> +};
> +
> +struct geni_i2c_clk_fld {
> +       u32     clk_freq_out;
> +       u8      clk_div;
> +       u8      t_high;
> +       u8      t_low;
> +       u8      t_cycle;
> +};
> +
> +static const struct geni_i2c_clk_fld geni_i2c_clk_map[] = {
> +       {KHz(100), 7, 10, 11, 26},
> +       {KHz(400), 2,  5, 12, 24},
> +       {KHz(1000), 1, 3,  9, 18},

So I guess this is all relying on an input serial clock of 19.2MHz?
Maybe document that?

Assuming I'm understanding the math here, is it really OK for your
100kHz and 1MHz mode to be running slightly fast?

19200. / 2 / 24
>>> 400.0

19200. / 7 / 26
>>> 105.49450549450549

19200. / 1 / 18
>>> 1066.6666666666667

It seems like you'd want the fastest clock that you can make that's
_less than_ the spec.


It would also be interesting to know if it's expected that boards
might need to tweak the t_high / t_low depending on their electrical
characteristics.  In the past I've had lots of requests from board
makers to tweak things because they've got a long trace, or a stronger
or weaker pull, or ...  If so we might later need to add some dts
properties like "i2c-scl-rising-time-ns" and make the math more
dynamic here, unless your hardware somehow automatically adjusts for
this type of thing...


> +};
> +
> +static int geni_i2c_clk_map_idx(struct geni_i2c_dev *gi2c)
> +{
> +       int i;
> +       const struct geni_i2c_clk_fld *itr = geni_i2c_clk_map;
> +
> +       for (i = 0; i < ARRAY_SIZE(geni_i2c_clk_map); i++, itr++) {
> +               if (itr->clk_freq_out == gi2c->clk_freq_out) {
> +                       gi2c->clk_fld = geni_i2c_clk_map + i;

Isn't "geni_i2c_clk_map + i" just "itr"?


> +                       return 0;
> +               }
> +       }
> +       return -EINVAL;
> +}
> +
> +static void qcom_geni_i2c_conf(struct geni_i2c_dev *gi2c)
> +{
> +       const struct geni_i2c_clk_fld *itr = gi2c->clk_fld;
> +       u32 val;
> +
> +       writel_relaxed(0, gi2c->se.base + SE_GENI_CLK_SEL);
> +
> +       val = (itr->clk_div << CLK_DIV_SHFT) | SER_CLK_EN;
> +       writel_relaxed(val, gi2c->se.base + GENI_SER_M_CLK_CFG);
> +
> +       val = itr->t_high << HIGH_COUNTER_SHFT;
> +       val |= itr->t_low << LOW_COUNTER_SHFT;
> +       val |= itr->t_cycle;
> +       writel_relaxed(val, gi2c->se.base + SE_I2C_SCL_COUNTERS);
> +       /*
> +        * Ensure later writes/reads to serial engine register block is
> +        * not reordered before this point.
> +        */
> +       mb();

This mb() is to make sure that later writes to "gi2c->se.base" are not
reordered to be above the ones in this function?  You don't need a
mb().  writel_relaxed() already enforces this.


> +}
> +
> +static void geni_i2c_err_misc(struct geni_i2c_dev *gi2c)
> +{
> +       u32 m_cmd = readl_relaxed(gi2c->se.base + SE_GENI_M_CMD0);
> +       u32 m_stat = readl_relaxed(gi2c->se.base + SE_GENI_M_IRQ_STATUS);
> +       u32 geni_s = readl_relaxed(gi2c->se.base + SE_GENI_STATUS);
> +       u32 geni_ios = readl_relaxed(gi2c->se.base + SE_GENI_IOS);
> +       u32 dma = readl_relaxed(gi2c->se.base + SE_GENI_DMA_MODE_EN);
> +       u32 rx_st, tx_st;
> +
> +       if (dma) {
> +               rx_st = readl_relaxed(gi2c->se.base + SE_DMA_RX_IRQ_STAT);
> +               tx_st = readl_relaxed(gi2c->se.base + SE_DMA_TX_IRQ_STAT);
> +       } else {
> +               rx_st = readl_relaxed(gi2c->se.base + SE_GENI_RX_FIFO_STATUS);
> +               tx_st = readl_relaxed(gi2c->se.base + SE_GENI_TX_FIFO_STATUS);
> +       }
> +       dev_dbg(gi2c->se.dev, "DMA:%d tx_stat:0x%x, rx_stat:0x%x, irq-stat:0x%x\n",
> +               dma, tx_st, rx_st, m_stat);
> +       dev_dbg(gi2c->se.dev, "m_cmd:0x%x, geni_status:0x%x, geni_ios:0x%x\n",
> +               m_cmd, geni_s, geni_ios);
> +}
> +
> +static void geni_i2c_err(struct geni_i2c_dev *gi2c, int err)
> +{
> +       gi2c->err = gi2c_log[err].err;

You should only set gi2c->err if it was 0 to start with.  You want
"err" to contain the first error, not the last one.  This is
especially important due to the comment elsewhere in this patch "if
this is err with done-bit not set, handle that through timeout".  You
don't want the timeout to clobber the true error.


On a separate note: I wonder if it makes sense to couch the rest of
this function in something that will compile to a no-op if DEBUG and
DYNAMIC_DEBUG aren't defined?  Then you can avoid including code for
all these readl calls.

> +       if (gi2c->cur)
> +               dev_dbg(gi2c->se.dev, "len:%d, slv-addr:0x%x, RD/WR:%d\n",
> +                       gi2c->cur->len, gi2c->cur->addr, gi2c->cur->flags);
> +       dev_dbg(gi2c->se.dev, "%s\n", gi2c_log[err].msg);
> +
> +       if (err != I2C_NACK && err != GENI_ABORT_DONE)
> +               geni_i2c_err_misc(gi2c);
> +}
> +
> +static irqreturn_t geni_i2c_irq(int irq, void *dev)
> +{
> +       struct geni_i2c_dev *gi2c = dev;
> +       int j;
> +       u32 m_stat = readl_relaxed(gi2c->se.base + SE_GENI_M_IRQ_STATUS);
> +       u32 rx_st = readl_relaxed(gi2c->se.base + SE_GENI_RX_FIFO_STATUS);
> +       u32 dm_tx_st = readl_relaxed(gi2c->se.base + SE_DMA_TX_IRQ_STAT);
> +       u32 dm_rx_st = readl_relaxed(gi2c->se.base + SE_DMA_RX_IRQ_STAT);
> +       u32 dma = readl_relaxed(gi2c->se.base + SE_GENI_DMA_MODE_EN);
> +       struct i2c_msg *cur = gi2c->cur;
> +
> +       if (!cur ||
> +           m_stat & (M_CMD_FAILURE_EN | M_CMD_ABORT_EN) ||
> +           dm_rx_st & (DM_I2C_CB_ERR)) {
> +               if (m_stat & M_GP_IRQ_1_EN)
> +                       geni_i2c_err(gi2c, I2C_NACK);
> +               if (m_stat & M_GP_IRQ_3_EN)
> +                       geni_i2c_err(gi2c, I2C_BUS_PROTO);
> +               if (m_stat & M_GP_IRQ_4_EN)
> +                       geni_i2c_err(gi2c, I2C_ARB_LOST);
> +               if (m_stat & M_CMD_OVERRUN_EN)
> +                       geni_i2c_err(gi2c, GENI_OVERRUN);
> +               if (m_stat & M_ILLEGAL_CMD_EN)
> +                       geni_i2c_err(gi2c, GENI_ILLEGAL_CMD);
> +               if (m_stat & M_CMD_ABORT_EN)
> +                       geni_i2c_err(gi2c, GENI_ABORT_DONE);
> +               if (m_stat & M_GP_IRQ_0_EN)
> +                       geni_i2c_err(gi2c, GP_IRQ0);
> +
> +               /* Disable the TX Watermark interrupt to stop TX */
> +               if (!dma)
> +                       writel_relaxed(0, gi2c->se.base +
> +                                          SE_GENI_TX_WATERMARK_REG);
> +               goto irqret;
> +       }
> +
> +       if (dma) {
> +               dev_dbg(gi2c->se.dev, "i2c dma tx:0x%x, dma rx:0x%x\n",
> +                       dm_tx_st, dm_rx_st);
> +               goto irqret;
> +       }
> +
> +       if (cur->flags & I2C_M_RD &&
> +           m_stat & (M_RX_FIFO_WATERMARK_EN | M_RX_FIFO_LAST_EN)) {
> +               u32 rxcnt = rx_st & RX_FIFO_WC_MSK;
> +
> +               for (j = 0; j < rxcnt; j++) {
> +                       u32 val;
> +                       int p = 0;
> +
> +                       val = readl_relaxed(gi2c->se.base + SE_GENI_RX_FIFOn);
> +                       while (gi2c->cur_rd < cur->len && p < sizeof(val)) {
> +                               cur->buf[gi2c->cur_rd++] = val & 0xff;
> +                               val >>= 8;
> +                               p++;
> +                       }
> +                       if (gi2c->cur_rd == cur->len)
> +                               break;
> +               }
> +       } else if (!(cur->flags & I2C_M_RD) &&
> +                  m_stat & M_TX_FIFO_WATERMARK_EN) {
> +               for (j = 0; j < gi2c->tx_wm; j++) {
> +                       u32 temp;
> +                       u32 val = 0;
> +                       int p = 0;
> +
> +                       while (gi2c->cur_wr < cur->len && p < sizeof(val)) {
> +                               temp = (u32)cur->buf[gi2c->cur_wr++];

What is the (u32) cast doing here?


> +                               val |= (temp << (p * 8));

Get rid of extra parenthesis.


> +                               p++;
> +                       }
> +                       writel_relaxed(val, gi2c->se.base + SE_GENI_TX_FIFOn);
> +                       /* TX Complete, Disable the TX Watermark interrupt */
> +                       if (gi2c->cur_wr == cur->len) {
> +                               writel_relaxed(0, gi2c->se.base +
> +                                               SE_GENI_TX_WATERMARK_REG);
> +                               break;
> +                       }
> +               }
> +       }
> +irqret:
> +       if (m_stat)
> +               writel_relaxed(m_stat, gi2c->se.base + SE_GENI_M_IRQ_CLEAR);
> +
> +       if (dma) {
> +               if (dm_tx_st)
> +                       writel_relaxed(dm_tx_st, gi2c->se.base +
> +                                               SE_DMA_TX_IRQ_CLR);
> +               if (dm_rx_st)
> +                       writel_relaxed(dm_rx_st, gi2c->se.base +
> +                                               SE_DMA_RX_IRQ_CLR);
> +       }
> +       /* if this is err with done-bit not set, handle that through timeout. */
> +       if (m_stat & M_CMD_DONE_EN)
> +               complete(&gi2c->done);
> +       else if ((dm_tx_st & TX_DMA_DONE) || (dm_rx_st & RX_DMA_DONE))
> +               complete(&gi2c->done);
> +
> +       return IRQ_HANDLED;
> +}
> +
> +static void geni_i2c_abort_xfer(struct geni_i2c_dev *gi2c)
> +{
> +       u32 val;
> +       unsigned long timeout = HZ;

Rename to time_left?  ...and maybe use a #define for the init value?


> +
> +       geni_i2c_err(gi2c, GENI_TIMEOUT);
> +       gi2c->cur = NULL;

Don't you need a spinlock or something?  In most of the other cases
you could get away with no locking because the irq isn't happening at
the same time as other code that's mucking with stuff, but in the
timeout case we may be mucking with stuff at the same time as the irq.


> +       geni_se_abort_m_cmd(&gi2c->se);
> +       do {
> +               timeout = wait_for_completion_timeout(&gi2c->done, timeout);
> +               val = readl_relaxed(gi2c->se.base + SE_GENI_M_IRQ_STATUS);
> +       } while (!(val & M_CMD_ABORT_EN) && timeout);

Print an error if there was a timeout aborting?


> +}
> +
> +static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> +                               u32 m_param)
> +{
> +       dma_addr_t rx_dma;
> +       enum geni_se_xfer_mode mode;
> +       unsigned long timeout;
> +
> +       gi2c->cur = msg;
> +       mode = msg->len > 32 ? GENI_SE_DMA : GENI_SE_FIFO;

DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
a lot by transferring i2c commands over DMA compared to a FIFO?
Enough to justify the code complexity and the set of bugs that will
show up?  I'm sure it will be a controversial assertion given that the
code's already written, but personally I'd be supportive of ripping
DMA mode out to simplify the driver.  I'd be curious if anyone else
agrees.  To me it seems like premature optimization.


> +       geni_se_select_mode(&gi2c->se, mode);
> +       writel_relaxed(msg->len, gi2c->se.base + SE_I2C_RX_TRANS_LEN);
> +       geni_se_setup_m_cmd(&gi2c->se, I2C_READ, m_param);
> +       if (mode == GENI_SE_DMA) {
> +               rx_dma = geni_se_rx_dma_prep(&gi2c->se, msg->buf, msg->len);

Randomly I noticed a flag called "I2C_M_DMA_SAFE".  Do we need to
check this flag before using msg->buf for DMA?  ...or use
i2c_get_dma_safe_msg_buf()?

...btw: the relative lack of people doing this in the kernel is
further evidence of DMA not really being worth it for i2c busses.


> +               if (!rx_dma) {
> +                       mode = GENI_SE_FIFO;
> +                       geni_se_select_mode(&gi2c->se, mode);
> +               }
> +       }
> +
> +       timeout = wait_for_completion_timeout(&gi2c->done, HZ);

Perhaps make a #define for the timeout instead of just hardcoding HZ (1 second).


> +       if (!timeout)

Can you rename "timeout" to "time_left"?  Otherwise this read like "if
there wasn't a timeout then abort".


> +               geni_i2c_abort_xfer(gi2c);
> +
> +       gi2c->cur_rd = 0;
> +       if (mode == GENI_SE_DMA) {
> +               if (gi2c->err) {
> +                       writel_relaxed(1, gi2c->se.base + SE_DMA_RX_FSM_RST);
> +                       wait_for_completion_timeout(&gi2c->done, HZ);

Worth printing an error if this one times out?  Seems like we'd be in
bad shape...

...also: to be paranoid do you need a re_init_completion before you
reset things?  In theory one could conceive of the concept that the
earlier completion timed out and then the DMA interrupt came right
after.  Now there will be a completion already on the books so your
wait will return instantly even though the reset hasn't been done.


> +               }
> +               geni_se_rx_dma_unprep(&gi2c->se, rx_dma, msg->len);
> +       }
> +       if (gi2c->err)
> +               dev_err(gi2c->se.dev, "i2c error :%d\n", gi2c->err);

OK, so I'm a bit baffled.  You've got all these tables in this driver
that give you nice/informative error messages.  Then those nice error
messages are just calling dev_dbg() and here you print out an arcane
linux error?

Also: seems like you wouldn't want to print errors for NACKs, right?
Otherwise i2cdetect is going to be spewing isn't it?


> +       return gi2c->err;
> +}
> +
> +static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> +                               u32 m_param)
> +{
> +       dma_addr_t tx_dma;
> +       enum geni_se_xfer_mode mode;
> +       unsigned long timeout;
> +
> +       gi2c->cur = msg;
> +       mode = msg->len > 32 ? GENI_SE_DMA : GENI_SE_FIFO;
> +       geni_se_select_mode(&gi2c->se, mode);
> +       writel_relaxed(msg->len, gi2c->se.base + SE_I2C_TX_TRANS_LEN);
> +       geni_se_setup_m_cmd(&gi2c->se, I2C_WRITE, m_param);
> +       if (mode == GENI_SE_DMA) {
> +               tx_dma = geni_se_tx_dma_prep(&gi2c->se, msg->buf, msg->len);
> +               if (!tx_dma) {
> +                       mode = GENI_SE_FIFO;
> +                       geni_se_select_mode(&gi2c->se, mode);
> +               }
> +       }
> +
> +       if (mode == GENI_SE_FIFO) /* Get FIFO IRQ */
> +               writel_relaxed(1, gi2c->se.base + SE_GENI_TX_WATERMARK_REG);
> +
> +       timeout = wait_for_completion_timeout(&gi2c->done, HZ);
> +       if (!timeout)
> +               geni_i2c_abort_xfer(gi2c);
> +
> +       gi2c->cur_wr = 0;
> +       if (mode == GENI_SE_DMA) {
> +               if (gi2c->err) {
> +                       writel_relaxed(1, gi2c->se.base + SE_DMA_TX_FSM_RST);
> +                       wait_for_completion_timeout(&gi2c->done, HZ);
> +               }
> +               geni_se_tx_dma_unprep(&gi2c->se, tx_dma, msg->len);
> +       }
> +       if (gi2c->err)
> +               dev_err(gi2c->se.dev, "i2c error :%d\n", gi2c->err);
> +       return gi2c->err;
> +}
> +
> +static int geni_i2c_xfer(struct i2c_adapter *adap,
> +                        struct i2c_msg msgs[],
> +                        int num)
> +{
> +       struct geni_i2c_dev *gi2c = i2c_get_adapdata(adap);
> +       int i, ret;
> +
> +       gi2c->err = 0;
> +       reinit_completion(&gi2c->done);
> +       ret = pm_runtime_get_sync(gi2c->se.dev);
> +       if (ret < 0) {
> +               dev_err(gi2c->se.dev, "error turning SE resources:%d\n", ret);
> +               pm_runtime_put_noidle(gi2c->se.dev);
> +               /* Set device in suspended since resume failed */
> +               pm_runtime_set_suspended(gi2c->se.dev);
> +               return ret;

Wow, that's a cluster of arcane calls to handle a call that probably
will never fail (it just enables clocks and sets pinctrl).  Sigh.
...but as far as I can tell the whole sequence is right.  You
definitely need a "put" after a failed get and it looks like
pm_runtime_set_suspended() has a special exception where it can be
called if you got a runtime error...


> +       }
> +
> +       qcom_geni_i2c_conf(gi2c);
> +       for (i = 0; i < num; i++) {
> +               u32 m_param = i < (num - 1) ? STOP_STRETCH : 0;
> +
> +               m_param |= ((msgs[i].addr << SLV_ADDR_SHFT) & SLV_ADDR_MSK);
> +
> +               if (msgs[i].flags & I2C_M_RD)
> +                       ret = geni_i2c_rx_one_msg(gi2c, &msgs[i], m_param);
> +               else
> +                       ret = geni_i2c_tx_one_msg(gi2c, &msgs[i], m_param);
> +
> +               if (ret) {
> +                       dev_err(gi2c->se.dev, "i2c error %d @ %d\n", ret, i);
> +                       break;
> +               }
> +       }
> +       if (ret == 0)
> +               ret = num;
> +
> +       pm_runtime_mark_last_busy(gi2c->se.dev);
> +       pm_runtime_put_autosuspend(gi2c->se.dev);
> +       gi2c->cur = NULL;
> +       gi2c->err = 0;
> +       return ret;
> +}
> +
> +static u32 geni_i2c_func(struct i2c_adapter *adap)
> +{
> +       return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
> +}
> +
> +static const struct i2c_algorithm geni_i2c_algo = {
> +       .master_xfer    = geni_i2c_xfer,
> +       .functionality  = geni_i2c_func,
> +};
> +
> +static int geni_i2c_probe(struct platform_device *pdev)
> +{
> +       struct geni_i2c_dev *gi2c;
> +       struct resource *res;
> +       u32 proto, tx_depth;
> +       int ret;
> +
> +       gi2c = devm_kzalloc(&pdev->dev, sizeof(*gi2c), GFP_KERNEL);
> +       if (!gi2c)
> +               return -ENOMEM;
> +
> +       gi2c->se.dev = &pdev->dev;
> +       gi2c->se.wrapper = dev_get_drvdata(pdev->dev.parent);
> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +       gi2c->se.base = devm_ioremap_resource(&pdev->dev, res);
> +       if (IS_ERR(gi2c->se.base)) {
> +               ret = PTR_ERR(gi2c->se.base);
> +               dev_err(&pdev->dev, "Err IO Mapping register block %d\n", ret);

No need for error message with devm_ioremap_resource().


> +               return ret;
> +       }
> +
> +       gi2c->se.clk = devm_clk_get(&pdev->dev, "se");
> +       if (IS_ERR(gi2c->se.clk)) {
> +               ret = PTR_ERR(gi2c->se.clk);
> +               dev_err(&pdev->dev, "Err getting SE Core clk %d\n", ret);
> +               return ret;
> +       }
> +
> +       ret = device_property_read_u32(&pdev->dev, "clock-frequency",
> +                                                       &gi2c->clk_freq_out);
> +       if (ret) {
> +               dev_info(&pdev->dev,
> +                       "Bus frequency not specified, default to 400KHz.\n");
> +               gi2c->clk_freq_out = KHz(400);
> +       }

I feel like it should default to 100KHz.  i2c_parse_fw_timings()
defaults to this and to me the wording "New drivers almost always
should use the defaults" makes me feel this should be the defaults.

> +
> +       gi2c->irq = platform_get_irq(pdev, 0);
> +       if (gi2c->irq < 0) {
> +               dev_err(&pdev->dev, "IRQ error for i2c-geni\n");
> +               return gi2c->irq;
> +       }
> +
> +       ret = geni_i2c_clk_map_idx(gi2c);
> +       if (ret) {
> +               dev_err(&pdev->dev, "Invalid clk frequency %d KHz: %d\n",
> +                       gi2c->clk_freq_out, ret);

Need a divide by 1000 since your printout includes "KHz".  Also note
that the proper Si units is kHz not KHz, isn't it?


> +               return ret;
> +       }
> +
> +       gi2c->adap.algo = &geni_i2c_algo;
> +       init_completion(&gi2c->done);
> +       platform_set_drvdata(pdev, gi2c);
> +       ret = devm_request_irq(&pdev->dev, gi2c->irq, geni_i2c_irq,
> +                              IRQF_TRIGGER_HIGH, "i2c_geni", gi2c);
> +       if (ret) {
> +               dev_err(&pdev->dev, "Request_irq failed:%d: err:%d\n",
> +                       gi2c->irq, ret);
> +               return ret;
> +       }
> +       disable_irq(gi2c->irq);

Can you explain the goal of the disable_irq() here.  Is it actually
needed for something or does it somehow save power?  From drivers I've
reviewed in the past this doesn't seem like a common thing to do, so
I'm curious what it's supposed to gain for you.  I'd be inclined to
just delete the whole disable/enable of the irq from this driver.


> +       i2c_set_adapdata(&gi2c->adap, gi2c);
> +       gi2c->adap.dev.parent = &pdev->dev;
> +       gi2c->adap.dev.of_node = pdev->dev.of_node;
> +       strlcpy(gi2c->adap.name, "Geni-I2C", sizeof(gi2c->adap.name));
> +
> +       ret = geni_se_resources_on(&gi2c->se);
> +       if (ret) {
> +               dev_err(&pdev->dev, "Error turning on resources %d\n", ret);
> +               return ret;
> +       }
> +       proto = geni_se_read_proto(&gi2c->se);
> +       tx_depth = geni_se_get_tx_fifo_depth(&gi2c->se);
> +       if (unlikely(proto != GENI_SE_I2C)) {

Avoid compiler hints like unlikely() unless you're really truly
optimizing a tight inner loop.  Otherwise let the compiler do its job.


> +               dev_err(&pdev->dev, "Invalid proto %d\n", proto);
> +               geni_se_resources_off(&gi2c->se);
> +               return -ENXIO;
> +       }
> +       gi2c->tx_wm = tx_depth - 1;
> +       geni_se_init(&gi2c->se, gi2c->tx_wm, tx_depth);
> +       geni_se_config_packing(&gi2c->se, BITS_PER_BYTE, PACKING_BYTES_PW,
> +                                                       true, true, true);
> +       geni_se_resources_off(&gi2c->se);
> +       dev_dbg(&pdev->dev, "i2c fifo/se-dma mode. fifo depth:%d\n", tx_depth);
> +
> +       pm_runtime_set_suspended(gi2c->se.dev);
> +       pm_runtime_set_autosuspend_delay(gi2c->se.dev, I2C_AUTO_SUSPEND_DELAY);
> +       pm_runtime_use_autosuspend(gi2c->se.dev);
> +       pm_runtime_enable(gi2c->se.dev);
> +       i2c_add_adapter(&gi2c->adap);
> +
> +       dev_dbg(&pdev->dev, "I2C probed\n");

Is this really a useful dev_dbg()?  Just turn on initcall debugging...


> +       return 0;
> +}
> +
> +static int geni_i2c_remove(struct platform_device *pdev)
> +{
> +       struct geni_i2c_dev *gi2c = platform_get_drvdata(pdev);
> +
> +       pm_runtime_disable(gi2c->se.dev);

Is this right?  You don't want to disable PM Runtime transitions but
you actually want to force the adapter into suspended state, don't
you?  I don't see anything that does that...


> +       i2c_del_adapter(&gi2c->adap);
> +       return 0;
> +}
> +
> +static int geni_i2c_resume_noirq(struct device *device)
> +{
> +       return 0;
> +}

No need for a dummy function; just stick NULL in the structure, no?

> +
> +#ifdef CONFIG_PM
> +static int geni_i2c_runtime_suspend(struct device *dev)
> +{
> +       struct geni_i2c_dev *gi2c = dev_get_drvdata(dev);
> +
> +       disable_irq(gi2c->irq);
> +       geni_se_resources_off(&gi2c->se);
> +       return 0;
> +}
> +
> +static int geni_i2c_runtime_resume(struct device *dev)
> +{
> +       int ret;
> +       struct geni_i2c_dev *gi2c = dev_get_drvdata(dev);
> +
> +       ret = geni_se_resources_on(&gi2c->se);
> +       if (ret)
> +               return ret;
> +
> +       enable_irq(gi2c->irq);
> +       return 0;
> +}
> +
> +static int geni_i2c_suspend_noirq(struct device *device)
> +{
> +       struct geni_i2c_dev *gi2c = dev_get_drvdata(device);
> +       int ret;
> +
> +       /* Make sure no transactions are pending */
> +       ret = i2c_trylock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
> +       if (!ret) {
> +               dev_err(gi2c->se.dev, "late I2C transaction request\n");
> +               return -EBUSY;
> +       }

Does this happen?  How?

Nothing about this code looks special for your hardware.  If this is
really needed, why is it not part of the i2c core since there's
nothing specific about your driver here?


> +       if (!pm_runtime_status_suspended(device)) {
> +               geni_i2c_runtime_suspend(device);
> +               pm_runtime_disable(device);
> +               pm_runtime_set_suspended(device);
> +               pm_runtime_enable(device);
> +       }

Similar question.  Why do you need this special case code?  Are there
cases where we're all the way at suspend_noirq and yet we still
haven't runtime suspended?  Can you please document how we get into
this state?


> +       i2c_unlock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
> +       return 0;
> +}
> +#else
> +static int geni_i2c_runtime_suspend(struct device *dev)
> +{
> +       return 0;
> +}
> +
> +static int geni_i2c_runtime_resume(struct device *dev)
> +{
> +       return 0;
> +}
> +
> +static int geni_i2c_suspend_noirq(struct device *device)
> +{
> +       return 0;
> +}
> +#endif
> +
> +static const struct dev_pm_ops geni_i2c_pm_ops = {
> +       .suspend_noirq          = geni_i2c_suspend_noirq,
> +       .resume_noirq           = geni_i2c_resume_noirq,
> +       .runtime_suspend        = geni_i2c_runtime_suspend,
> +       .runtime_resume         = geni_i2c_runtime_resume,

Please use SET_NOIRQ_SYSTEM_SLEEP_PM_OPS and SET_RUNTIME_PM_OPS.  Then
you can get rid of all the dummy functions.  AKA something like:

static const struct dev_pm_ops geni_i2c_pm_ops = {
  SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(geni_i2c_suspend_noirq, NULL)
  SET_RUNTIME_PM_OPS(geni_i2c_runtime_suspend, geni_i2c_runtime_resume, NULL)
};


> +};
> +
> +static const struct of_device_id geni_i2c_dt_match[] = {
> +       { .compatible = "qcom,geni-i2c" },
> +       {}
> +};
> +MODULE_DEVICE_TABLE(of, geni_i2c_dt_match);
> +
> +static struct platform_driver geni_i2c_driver = {
> +       .probe  = geni_i2c_probe,
> +       .remove = geni_i2c_remove,
> +       .driver = {
> +               .name = "geni_i2c",
> +               .pm = &geni_i2c_pm_ops,
> +               .of_match_table = geni_i2c_dt_match,
> +       },
> +};
> +
> +module_platform_driver(geni_i2c_driver);
> +
> +MODULE_DESCRIPTION("I2C Controller Driver for GENI based QUP cores");
> +MODULE_LICENSE("GPL v2");
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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Sagar Dharia]

Hi Doug,
Thank you for reviewing the patch. I will take a stab at a few comments 
below. We will address most of the other comments in next version of I2C 
patch.
> 
> 
>> +
>> +#define I2C_AUTO_SUSPEND_DELAY 250
> 
> Why 250 ms?  That seems like an eternity.  Is it really that expensive
> to turn resources off and on?  I would sorta just expect clocks and
> stuff to get turned off right after a transaction finished unless
> another one was pending right behind it...
> 
The response from RPMh to turn on/off shared resources also take quite a 
few msecs. The QUP serial bus block sits quite a few shared-NOCs away 
from the memory and runtime-PM is used a bandwidth vote/NOC vote for 
these NOCs from QUP to memory. Also the RPC between apps and RPMh can 
sometimes take longer depending on other tasks running on apps. This 250 
msec avoids thrashing of these RPCs between apps and RPMh.
If you plan to keep these NOCs on forever, then your are right: 
runtime-PM will be only used to turn on/off local clocks and we won't 
even need autosuspend. that's not true on products where this driver is 
currently deployed.
>> +
>> +static const struct geni_i2c_clk_fld geni_i2c_clk_map[] = {
>> +       {KHz(100), 7, 10, 11, 26},
>> +       {KHz(400), 2,  5, 12, 24},
>> +       {KHz(1000), 1, 3,  9, 18},
> 
> So I guess this is all relying on an input serial clock of 19.2MHz?
> Maybe document that?
> 
> Assuming I'm understanding the math here, is it really OK for your
> 100kHz and 1MHz mode to be running slightly fast?
> 
> 19200. / 2 / 24
>>>> 400.0
> 
> 19200. / 7 / 26
>>>> 105.49450549450549
> 
> 19200. / 1 / 18
>>>> 1066.6666666666667
> 
> It seems like you'd want the fastest clock that you can make that's
> _less than_ the spec.
> 
> 
> It would also be interesting to know if it's expected that boards
> might need to tweak the t_high / t_low depending on their electrical
> characteristics.  In the past I've had lots of requests from board
> makers to tweak things because they've got a long trace, or a stronger
> or weaker pull, or ...  If so we might later need to add some dts
> properties like "i2c-scl-rising-time-ns" and make the math more
> dynamic here, unless your hardware somehow automatically adjusts for
> this type of thing...
>These values are derived by our HW team to comply with the t-high and 
t-low specs of I2C. We have confirmed on scope that the frequency of SCL 
is indeed less than/equal to the spec. We have not come across slaves 
who have needed to tweak these things. We are open to adding these 
properties in dts if you have any such slaves not conforming due to 
board-layout of other reasons.
>> +       mode = msg->len > 32 ? GENI_SE_DMA : GENI_SE_FIFO;
> 
> DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
> a lot by transferring i2c commands over DMA compared to a FIFO?
> Enough to justify the code complexity and the set of bugs that will
> show up?  I'm sure it will be a controversial assertion given that the
> code's already written, but personally I'd be supportive of ripping
> DMA mode out to simplify the driver.  I'd be curious if anyone else
> agrees.  To me it seems like premature optimization.

Yes, we have multiple clients (e.g. touch, NFC) using I2C for data 
transfers bigger than 32 bytes (some transfers are 100s of bytes). The 
fifo size is 32, so we can definitely avoid at least 1 interrupt when 
DMA mode is used with data size > 32.
> 
> 
>> +       geni_se_select_mode(&gi2c->se, mode);
>> +       writel_relaxed(msg->len, gi2c->se.base + SE_I2C_RX_TRANS_LEN);
>> +       geni_se_setup_m_cmd(&gi2c->se, I2C_READ, m_param);
>> +       if (mode == GENI_SE_DMA) {
>> +               rx_dma = geni_se_rx_dma_prep(&gi2c->se, msg->buf, msg->len);
> 
> Randomly I noticed a flag called "I2C_M_DMA_SAFE".  Do we need to
> check this flag before using msg->buf for DMA?  ...or use
> i2c_get_dma_safe_msg_buf()?
> 
> ...btw: the relative lack of people doing this in the kernel is
> further evidence of DMA not really being worth it for i2c busses.
I cannot comment about other drivers here using or not using DMA since 
they may not be exercised with slaves like NFC?
>> +       ret = pm_runtime_get_sync(gi2c->se.dev);
>> +       if (ret < 0) {
>> +               dev_err(gi2c->se.dev, "error turning SE resources:%d\n", ret);
>> +               pm_runtime_put_noidle(gi2c->se.dev);
>> +               /* Set device in suspended since resume failed */
>> +               pm_runtime_set_suspended(gi2c->se.dev);
>> +               return ret;
> 
> Wow, that's a cluster of arcane calls to handle a call that probably
> will never fail (it just enables clocks and sets pinctrl).  Sigh.
> ...but as far as I can tell the whole sequence is right.  You
> definitely need a "put" after a failed get and it looks like
> pm_runtime_set_suspended() has a special exception where it can be
> called if you got a runtime error...
We didn't have this in before either. But this condition is somewhat 
frequent if I2C transactions are called on cusp of exiting system 
suspend. (e.g. PMIC slave getting a wakeup-IRQ and trying to read from 
PMIC through I2C to read its status as to what caused that wake-up. At 
that time, get_sync doesn't really enable resources (kernel 4.9) since 
the runtime-pm ref-count isn't decremented. We run the risk of unclocked 
access if these arcane calls aren't present. You can go through 
runtime-pm documentation chapter 6 for more details.

>> +       ret = devm_request_irq(&pdev->dev, gi2c->irq, geni_i2c_irq,
>> +                              IRQF_TRIGGER_HIGH, "i2c_geni", gi2c);
>> +       if (ret) {
>> +               dev_err(&pdev->dev, "Request_irq failed:%d: err:%d\n",
>> +                       gi2c->irq, ret);
>> +               return ret;
>> +       }
>> +       disable_irq(gi2c->irq);
> 
> Can you explain the goal of the disable_irq() here.  Is it actually
> needed for something or does it somehow save power?  From drivers I've
> reviewed in the past this doesn't seem like a common thing to do, so
> I'm curious what it's supposed to gain for you.  I'd be inclined to
> just delete the whole disable/enable of the irq from this driver.

Qualcomm's power team suggests we enable/disable unused IRQs. Otherwise 
they can block apps from entering some low-power mode (unless the 
interrupt is in some list?) I will confirm again with them and let you know.
>> +       /* Make sure no transactions are pending */
>> +       ret = i2c_trylock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
>> +       if (!ret) {
>> +               dev_err(gi2c->se.dev, "late I2C transaction request\n");
>> +               return -EBUSY;
>> +       }
> 
> Does this happen?  How?
> 
> Nothing about this code looks special for your hardware.  If this is
> really needed, why is it not part of the i2c core since there's
> nothing specific about your driver here?
> 
There have been some clients that don't implement sys-suspend/resume 
callbacks (so i2c adapter has no clue they are done with their 
transactions) and this allows us to be flexible when they call I2C 
transactions extremely late.

> 
>> +       if (!pm_runtime_status_suspended(device)) {
>> +               geni_i2c_runtime_suspend(device);
>> +               pm_runtime_disable(device);
>> +               pm_runtime_set_suspended(device);
>> +               pm_runtime_enable(device);
>> +       }
> 
> Similar question.  Why do you need this special case code?  Are there
> cases where we're all the way at suspend_noirq and yet we still
> haven't runtime suspended?  Can you please document how we get into
> this state?
> This is when transaction happens less-than 250 msec of the 
system-suspend. PM-runtime has not gotten a chance to auto-suspend us 
since timer hasn't expired before system-suspend is attempted. These 
calls make sure that we truly turn off driver resources and make 
runtime-PM state consistent with the HW state. We can document this.


Thanks
Sagar
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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Doug Anderson]

Hi,

On Wed, Mar 7, 2018 at 6:42 PM, Sagar Dharia <sdharia@codeaurora.org> wrote:
> Hi Doug,
> Thank you for reviewing the patch. I will take a stab at a few comments
> below. We will address most of the other comments in next version of I2C
> patch.
>>
>>
>>
>>> +
>>> +#define I2C_AUTO_SUSPEND_DELAY 250
>>
>>
>> Why 250 ms?  That seems like an eternity.  Is it really that expensive
>> to turn resources off and on?  I would sorta just expect clocks and
>> stuff to get turned off right after a transaction finished unless
>> another one was pending right behind it...
>>
> The response from RPMh to turn on/off shared resources also take quite a few
> msecs. The QUP serial bus block sits quite a few shared-NOCs away from the
> memory and runtime-PM is used a bandwidth vote/NOC vote for these NOCs from
> QUP to memory. Also the RPC between apps and RPMh can sometimes take longer
> depending on other tasks running on apps. This 250 msec avoids thrashing of
> these RPCs between apps and RPMh.
> If you plan to keep these NOCs on forever, then your are right: runtime-PM
> will be only used to turn on/off local clocks and we won't even need
> autosuspend. that's not true on products where this driver is currently
> deployed.

OK, fair enough.  I don't know how RPMh works well enough to argue.
It does seem odd that you'd want to design things such that it takes a
few msecs to pull it out of runtime suspend, especially for touch.


>>> +
>>> +static const struct geni_i2c_clk_fld geni_i2c_clk_map[] = {
>>> +       {KHz(100), 7, 10, 11, 26},
>>> +       {KHz(400), 2,  5, 12, 24},
>>> +       {KHz(1000), 1, 3,  9, 18},
>>
>>
>> So I guess this is all relying on an input serial clock of 19.2MHz?
>> Maybe document that?
>>
>> Assuming I'm understanding the math here, is it really OK for your
>> 100kHz and 1MHz mode to be running slightly fast?
>>
>> 19200. / 2 / 24
>>>>>
>>>>> 400.0
>>
>>
>> 19200. / 7 / 26
>>>>>
>>>>> 105.49450549450549
>>
>>
>> 19200. / 1 / 18
>>>>>
>>>>> 1066.6666666666667
>>
>>
>> It seems like you'd want the fastest clock that you can make that's
>> _less than_ the spec.
>>
>>
>> It would also be interesting to know if it's expected that boards
>> might need to tweak the t_high / t_low depending on their electrical
>> characteristics.  In the past I've had lots of requests from board
>> makers to tweak things because they've got a long trace, or a stronger
>> or weaker pull, or ...  If so we might later need to add some dts
>> properties like "i2c-scl-rising-time-ns" and make the math more
>> dynamic here, unless your hardware somehow automatically adjusts for
>> this type of thing...
>> These values are derived by our HW team to comply with the t-high and
>
> t-low specs of I2C. We have confirmed on scope that the frequency of SCL is
> indeed less than/equal to the spec. We have not come across slaves who have
> needed to tweak these things. We are open to adding these properties in dts
> if you have any such slaves not conforming due to board-layout of other
> reasons.

OK, I'm fine with leaving something like this till later if/when it
comes up.  Documenting a little bit more about how these timings work
seems like it would be nice, though, at least mentioning what the
source clock is...


>>>
>>> +       mode = msg->len > 32 ? GENI_SE_DMA : GENI_SE_FIFO;
>>
>>
>> DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
>> a lot by transferring i2c commands over DMA compared to a FIFO?
>> Enough to justify the code complexity and the set of bugs that will
>> show up?  I'm sure it will be a controversial assertion given that the
>> code's already written, but personally I'd be supportive of ripping
>> DMA mode out to simplify the driver.  I'd be curious if anyone else
>> agrees.  To me it seems like premature optimization.
>
>
> Yes, we have multiple clients (e.g. touch, NFC) using I2C for data transfers
> bigger than 32 bytes (some transfers are 100s of bytes). The fifo size is
> 32, so we can definitely avoid at least 1 interrupt when DMA mode is used
> with data size > 32.

Does that 1-2 interrupts make any real difference, though?  In theory
it really shouldn't affect the transfer rate.  We should be able to
service the interrupt plenty fast and if we were concerned we would
tweak the watermark code a little bit.  So I guess we're worried about
the extra CPU cycles (and power cost) to service those extra couple
interrupts?

In theory when touch data is coming in or NFC data is coming in then
we're probably not in a super low power state to begin with.  If it's
touch data we likely want to have the CPU boosted a bunch to respond
to the user quickly.  If we've got 8 cores available all of which can
run at 1GHz or more a few interrupts won't kill us.  NFC data is
probably not common enough that we need to optimize power/CPU
utilizatoin for that.


So while i can believe that you do save an interrupt or two, I still
am not convinced that those interrupts are worth a bunch of complex
code (and a whole second code path) to save.


...also note that above you said that coming out of runtime suspend
can take several msec.  That seems like it dwarfs any slight
difference in timing between a FIFO-based operation and DMA.


>>> +       geni_se_select_mode(&gi2c->se, mode);
>>> +       writel_relaxed(msg->len, gi2c->se.base + SE_I2C_RX_TRANS_LEN);
>>> +       geni_se_setup_m_cmd(&gi2c->se, I2C_READ, m_param);
>>> +       if (mode == GENI_SE_DMA) {
>>> +               rx_dma = geni_se_rx_dma_prep(&gi2c->se, msg->buf,
>>> msg->len);
>>
>>
>> Randomly I noticed a flag called "I2C_M_DMA_SAFE".  Do we need to
>> check this flag before using msg->buf for DMA?  ...or use
>> i2c_get_dma_safe_msg_buf()?
>>
>> ...btw: the relative lack of people doing this in the kernel is
>> further evidence of DMA not really being worth it for i2c busses.
>
> I cannot comment about other drivers here using or not using DMA since they
> may not be exercised with slaves like NFC?
>>>
>>> +       ret = pm_runtime_get_sync(gi2c->se.dev);
>>> +       if (ret < 0) {
>>> +               dev_err(gi2c->se.dev, "error turning SE resources:%d\n",
>>> ret);
>>> +               pm_runtime_put_noidle(gi2c->se.dev);
>>> +               /* Set device in suspended since resume failed */
>>> +               pm_runtime_set_suspended(gi2c->se.dev);
>>> +               return ret;
>>
>>
>> Wow, that's a cluster of arcane calls to handle a call that probably
>> will never fail (it just enables clocks and sets pinctrl).  Sigh.
>> ...but as far as I can tell the whole sequence is right.  You
>> definitely need a "put" after a failed get and it looks like
>> pm_runtime_set_suspended() has a special exception where it can be
>> called if you got a runtime error...
>
> We didn't have this in before either. But this condition is somewhat
> frequent if I2C transactions are called on cusp of exiting system suspend.
> (e.g. PMIC slave getting a wakeup-IRQ and trying to read from PMIC through
> I2C to read its status as to what caused that wake-up. At that time,
> get_sync doesn't really enable resources (kernel 4.9) since the runtime-pm
> ref-count isn't decremented. We run the risk of unclocked access if these
> arcane calls aren't present. You can go through runtime-pm documentation
> chapter 6 for more details.

Yeah, I certainly agree that the calls are needed if
pm_runtime_get_sync() and I'm not suggesting removing them.  Hence the
"as far as I can tell the whole sequence is right".

...but I'm actually kinda worried if you're saying that you actually
ran into this case.  Hopefully that got fixed and code no longer tries
to read from the PMIC at a bad time anymore?  That code should be
fixed not to be running so late in suspend.


>>> +       ret = devm_request_irq(&pdev->dev, gi2c->irq, geni_i2c_irq,
>>> +                              IRQF_TRIGGER_HIGH, "i2c_geni", gi2c);
>>> +       if (ret) {
>>> +               dev_err(&pdev->dev, "Request_irq failed:%d: err:%d\n",
>>> +                       gi2c->irq, ret);
>>> +               return ret;
>>> +       }
>>> +       disable_irq(gi2c->irq);
>>
>>
>> Can you explain the goal of the disable_irq() here.  Is it actually
>> needed for something or does it somehow save power?  From drivers I've
>> reviewed in the past this doesn't seem like a common thing to do, so
>> I'm curious what it's supposed to gain for you.  I'd be inclined to
>> just delete the whole disable/enable of the irq from this driver.
>
>
> Qualcomm's power team suggests we enable/disable unused IRQs. Otherwise they
> can block apps from entering some low-power mode (unless the interrupt is in
> some list?) I will confirm again with them and let you know.

Since this is weird (to me anyway), please document w/ a comment.


>>>
>>> +       /* Make sure no transactions are pending */
>>> +       ret = i2c_trylock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
>>> +       if (!ret) {
>>> +               dev_err(gi2c->se.dev, "late I2C transaction request\n");
>>> +               return -EBUSY;
>>> +       }
>>
>>
>> Does this happen?  How?
>>
>> Nothing about this code looks special for your hardware.  If this is
>> really needed, why is it not part of the i2c core since there's
>> nothing specific about your driver here?
>>
> There have been some clients that don't implement sys-suspend/resume
> callbacks (so i2c adapter has no clue they are done with their transactions)
> and this allows us to be flexible when they call I2C transactions extremely
> late.

Still feels like this belongs in the i2c core, not your driver.  Maybe
you should send a patch for the core and remove it from here?

...and also, it seems like any i2c clients that don't implement the
suspend/resume callbacks and try to do i2c transactions late in the
game need to be fixed.  It should be documented that this isn't a
valid thing for a driver to do and if we end up in this error case
then it's not an i2c issue but it's a bad driver somewhere.

>
>>
>>> +       if (!pm_runtime_status_suspended(device)) {
>>> +               geni_i2c_runtime_suspend(device);
>>> +               pm_runtime_disable(device);
>>> +               pm_runtime_set_suspended(device);
>>> +               pm_runtime_enable(device);
>>> +       }
>>
>>
>> Similar question.  Why do you need this special case code?  Are there
>> cases where we're all the way at suspend_noirq and yet we still
>> haven't runtime suspended?  Can you please document how we get into
>> this state?
>> This is when transaction happens less-than 250 msec of the
>
> system-suspend. PM-runtime has not gotten a chance to auto-suspend us since
> timer hasn't expired before system-suspend is attempted. These calls make
> sure that we truly turn off driver resources and make runtime-PM state
> consistent with the HW state. We can document this.

OK.  PM Runtime always gets me mixed up.  Seems really strange that it
wouldn't autosuspend all devices (regardless of timeout) at system
suspend time.

-Doug
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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Doug Anderson]

Hi,

On Wed, Mar 7, 2018 at 9:19 PM, Doug Anderson <dianders@chromium.org> wrote:
>>> DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
>>> a lot by transferring i2c commands over DMA compared to a FIFO?
>>> Enough to justify the code complexity and the set of bugs that will
>>> show up?  I'm sure it will be a controversial assertion given that the
>>> code's already written, but personally I'd be supportive of ripping
>>> DMA mode out to simplify the driver.  I'd be curious if anyone else
>>> agrees.  To me it seems like premature optimization.
>>
>>
>> Yes, we have multiple clients (e.g. touch, NFC) using I2C for data transfers
>> bigger than 32 bytes (some transfers are 100s of bytes). The fifo size is
>> 32, so we can definitely avoid at least 1 interrupt when DMA mode is used
>> with data size > 32.
>
> Does that 1-2 interrupts make any real difference, though?  In theory
> it really shouldn't affect the transfer rate.  We should be able to
> service the interrupt plenty fast and if we were concerned we would
> tweak the watermark code a little bit.  So I guess we're worried about
> the extra CPU cycles (and power cost) to service those extra couple
> interrupts?
>
> In theory when touch data is coming in or NFC data is coming in then
> we're probably not in a super low power state to begin with.  If it's
> touch data we likely want to have the CPU boosted a bunch to respond
> to the user quickly.  If we've got 8 cores available all of which can
> run at 1GHz or more a few interrupts won't kill us.  NFC data is
> probably not common enough that we need to optimize power/CPU
> utilizatoin for that.
>
>
> So while i can believe that you do save an interrupt or two, I still
> am not convinced that those interrupts are worth a bunch of complex
> code (and a whole second code path) to save.
>
>
> ...also note that above you said that coming out of runtime suspend
> can take several msec.  That seems like it dwarfs any slight
> difference in timing between a FIFO-based operation and DMA.

One last note here (sorry for not thinking of this last night) is that
I would also be interested in considering _only_ supporting the DMA
path.  Is it somehow intrinsically bad to use the DMA flow for a
1-byte transfer?  Is there a bunch of extra overhead or power draw?

Specifically my main point is that maintaining two separate flows (the
FIFO flow vs the DMA flow) adds complexity, code size, and bugs.  If
there's a really good reason to maintain both flows then fine, but we
should really consider if this is something that's really giving us
value before we agree to it.


-Doug
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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Sagar Dharia]

Hi Doug

On 3/8/2018 2:12 PM, Doug Anderson wrote:
> Hi,
> 
> On Wed, Mar 7, 2018 at 9:19 PM, Doug Anderson <dianders@chromium.org> wrote:
>>>> DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
>>>> a lot by transferring i2c commands over DMA compared to a FIFO?
>>>> Enough to justify the code complexity and the set of bugs that will
>>>> show up?  I'm sure it will be a controversial assertion given that the
>>>> code's already written, but personally I'd be supportive of ripping
>>>> DMA mode out to simplify the driver.  I'd be curious if anyone else
>>>> agrees.  To me it seems like premature optimization.
>>>
>>>
>>> Yes, we have multiple clients (e.g. touch, NFC) using I2C for data transfers
>>> bigger than 32 bytes (some transfers are 100s of bytes). The fifo size is
>>> 32, so we can definitely avoid at least 1 interrupt when DMA mode is used
>>> with data size > 32.
>>
>> Does that 1-2 interrupts make any real difference, though?  In theory
>> it really shouldn't affect the transfer rate.  We should be able to
>> service the interrupt plenty fast and if we were concerned we would
>> tweak the watermark code a little bit.  So I guess we're worried about
>> the extra CPU cycles (and power cost) to service those extra couple
>> interrupts?
>>
>> In theory when touch data is coming in or NFC data is coming in then
>> we're probably not in a super low power state to begin with.  If it's
>> touch data we likely want to have the CPU boosted a bunch to respond
>> to the user quickly.  If we've got 8 cores available all of which can
>> run at 1GHz or more a few interrupts won't kill us.  NFC data is
>> probably not common enough that we need to optimize power/CPU
>> utilizatoin for that.
>>
>>
>> So while i can believe that you do save an interrupt or two, I still
>> am not convinced that those interrupts are worth a bunch of complex
>> code (and a whole second code path) to save.
>>
>>
>> ...also note that above you said that coming out of runtime suspend
>> can take several msec.  That seems like it dwarfs any slight
>> difference in timing between a FIFO-based operation and DMA.
> 
> One last note here (sorry for not thinking of this last night) is that
> I would also be interested in considering _only_ supporting the DMA
> path.  Is it somehow intrinsically bad to use the DMA flow for a
> 1-byte transfer?  Is there a bunch of extra overhead or power draw?
> 
> Specifically my main point is that maintaining two separate flows (the
> FIFO flow vs the DMA flow) adds complexity, code size, and bugs.  If
> there's a really good reason to maintain both flows then fine, but we
> should really consider if this is something that's really giving us
> value before we agree to it.
> 

FIFO mode gives us 2 advantages:
1. small transfers don't have to go through 'dma-map/unmap penalties.
Some small buffers come from the stack of client caller and the
dma-map/unmap may fail.
2. bring-ups are 'less eventful' (with temp. change to just not have DMA
mode at all during bring-ups) since SMMU translation/DMA path from QUP
(master) to memory slave may not always available when critical I2C
peripherals need to be brought up (e.g. PMIC). CPU to QUP (slave) path
is usually available.

On the other side, DMA mode has other advantages:
1. Multiple android clients are still heavily using I2C in spite of
faster peripheral buses being available in industry.
As an example, some multi-finger Touch screens use I2C and the data to
be transferred per transaction over the bus grows well beyond 70-100
bytes based on number of fingers. These transactions are very frequent
when touch is being used, and in an environment where other heavy system
users are also running (MM/graphics).
Another example is, NFC uses I2C (as of now) to transfer as much as 700+
bytes. This can save us 20+ interrupts per transfer.

These transfers are mostly in burst. So the RPMh penalty to resume the
shared resources is only experienced for very first transfer. Remaining
transfers in the burst benefit from DMA if they are too big.

Goal here is to have common driver for upstream targets and android and
android has seen proven advantages with both modes.
If we end up keeping DMA only for downstream (or FIFO only for
downstream), then we lose the advantage of having code in upstream since
we have to maintain downstream patch with other mode.

Thanks
Sagar

> 
> -Doug
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-- 
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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Doug Anderson]

Hi,

On Thu, Mar 8, 2018 at 5:06 PM, Sagar Dharia <sdharia@codeaurora.org> wrote:
> Hi Doug
>
>
> On 3/8/2018 2:12 PM, Doug Anderson wrote:
>>
>> Hi,
>>
>> On Wed, Mar 7, 2018 at 9:19 PM, Doug Anderson <dianders@chromium.org>
>> wrote:
>>>>>
>>>>> DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
>>>>> a lot by transferring i2c commands over DMA compared to a FIFO?
>>>>> Enough to justify the code complexity and the set of bugs that will
>>>>> show up?  I'm sure it will be a controversial assertion given that the
>>>>> code's already written, but personally I'd be supportive of ripping
>>>>> DMA mode out to simplify the driver.  I'd be curious if anyone else
>>>>> agrees.  To me it seems like premature optimization.
>>>>
>>>>
>>>>
>>>> Yes, we have multiple clients (e.g. touch, NFC) using I2C for data
>>>> transfers
>>>> bigger than 32 bytes (some transfers are 100s of bytes). The fifo size
>>>> is
>>>> 32, so we can definitely avoid at least 1 interrupt when DMA mode is
>>>> used
>>>> with data size > 32.
>>>
>>>
>>> Does that 1-2 interrupts make any real difference, though?  In theory
>>> it really shouldn't affect the transfer rate.  We should be able to
>>> service the interrupt plenty fast and if we were concerned we would
>>> tweak the watermark code a little bit.  So I guess we're worried about
>>> the extra CPU cycles (and power cost) to service those extra couple
>>> interrupts?
>>>
>>> In theory when touch data is coming in or NFC data is coming in then
>>> we're probably not in a super low power state to begin with.  If it's
>>> touch data we likely want to have the CPU boosted a bunch to respond
>>> to the user quickly.  If we've got 8 cores available all of which can
>>> run at 1GHz or more a few interrupts won't kill us.  NFC data is
>>> probably not common enough that we need to optimize power/CPU
>>> utilizatoin for that.
>>>
>>>
>>> So while i can believe that you do save an interrupt or two, I still
>>> am not convinced that those interrupts are worth a bunch of complex
>>> code (and a whole second code path) to save.
>>>
>>>
>>> ...also note that above you said that coming out of runtime suspend
>>> can take several msec.  That seems like it dwarfs any slight
>>> difference in timing between a FIFO-based operation and DMA.
>>
>>
>> One last note here (sorry for not thinking of this last night) is that
>> I would also be interested in considering _only_ supporting the DMA
>> path.  Is it somehow intrinsically bad to use the DMA flow for a
>> 1-byte transfer?  Is there a bunch of extra overhead or power draw?
>>
>> Specifically my main point is that maintaining two separate flows (the
>> FIFO flow vs the DMA flow) adds complexity, code size, and bugs.  If
>> there's a really good reason to maintain both flows then fine, but we
>> should really consider if this is something that's really giving us
>> value before we agree to it.
>>
>
> FIFO mode gives us 2 advantages:
> 1. small transfers don't have to go through 'dma-map/unmap penalties.
> Some small buffers come from the stack of client caller and the
> dma-map/unmap may fail.
> 2. bring-ups are 'less eventful' (with temp. change to just not have DMA
> mode at all during bring-ups) since SMMU translation/DMA path from QUP
> (master) to memory slave may not always available when critical I2C
> peripherals need to be brought up (e.g. PMIC). CPU to QUP (slave) path
> is usually available.
>
> On the other side, DMA mode has other advantages:
> 1. Multiple android clients are still heavily using I2C in spite of
> faster peripheral buses being available in industry.
> As an example, some multi-finger Touch screens use I2C and the data to
> be transferred per transaction over the bus grows well beyond 70-100
> bytes based on number of fingers. These transactions are very frequent
> when touch is being used, and in an environment where other heavy system
> users are also running (MM/graphics).
> Another example is, NFC uses I2C (as of now) to transfer as much as 700+
> bytes. This can save us 20+ interrupts per transfer.
>
> These transfers are mostly in burst. So the RPMh penalty to resume the
> shared resources is only experienced for very first transfer. Remaining
> transfers in the burst benefit from DMA if they are too big.
>
> Goal here is to have common driver for upstream targets and android and
> android has seen proven advantages with both modes.
> If we end up keeping DMA only for downstream (or FIFO only for
> downstream), then we lose the advantage of having code in upstream since
> we have to maintain downstream patch with other mode.

OK, fair enough.  Having DMA mode alone would be a pain at bringup if
nothing else.  You're right.

I would still argue that perhaps those extra interrupts for FIFO mode
aren't quite as bit of a deal as you're making it out to be.  I've
been on systems that get massive number of interrupts almost
constantly and really it wasn't noticeable.

In any case, I didn't think I'd really convince anyone with this one,
so unless someone out there who matters actually feels the same way as
me then feel free to just ignore this and keep supporting both DMA and
FIFO mode.


-Doug
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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Sagar Dharia]

Hi Doug,

On 3/7/2018 10:19 PM, Doug Anderson wrote:
> Hi,
> 
> On Wed, Mar 7, 2018 at 6:42 PM, Sagar Dharia <sdharia@codeaurora.org> wrote:
>> Hi Doug,
>> Thank you for reviewing the patch. I will take a stab at a few comments
>> below. We will address most of the other comments in next version of I2C
>> patch.
>>>
>>>> +
>>>> +static const struct geni_i2c_clk_fld geni_i2c_clk_map[] = {
>>>> +       {KHz(100), 7, 10, 11, 26},
>>>> +       {KHz(400), 2,  5, 12, 24},
>>>> +       {KHz(1000), 1, 3,  9, 18},
>>>
>>>
>>> So I guess this is all relying on an input serial clock of 19.2MHz?
>>> Maybe document that?
>>>
>>> Assuming I'm understanding the math here, is it really OK for your
>>> 100kHz and 1MHz mode to be running slightly fast?
>>>
>>> 19200. / 2 / 24
>>>>>>
>>>>>> 400.0
>>>
>>>
>>> 19200. / 7 / 26
>>>>>>
>>>>>> 105.49450549450549
>>>
>>>
>>> 19200. / 1 / 18
>>>>>>
>>>>>> 1066.6666666666667
>>>
>>>
>>> It seems like you'd want the fastest clock that you can make that's
>>> _less than_ the spec.
>>>
>>>
>>> It would also be interesting to know if it's expected that boards
>>> might need to tweak the t_high / t_low depending on their electrical
>>> characteristics.  In the past I've had lots of requests from board
>>> makers to tweak things because they've got a long trace, or a stronger
>>> or weaker pull, or ...  If so we might later need to add some dts
>>> properties like "i2c-scl-rising-time-ns" and make the math more
>>> dynamic here, unless your hardware somehow automatically adjusts for
>>> this type of thing...
>>> These values are derived by our HW team to comply with the t-high and
>>
>> t-low specs of I2C. We have confirmed on scope that the frequency of SCL is
>> indeed less than/equal to the spec. We have not come across slaves who have
>> needed to tweak these things. We are open to adding these properties in dts
>> if you have any such slaves not conforming due to board-layout of other
>> reasons.
> 
> OK, I'm fine with leaving something like this till later if/when it
> comes up.  Documenting a little bit more about how these timings work
> seems like it would be nice, though, at least mentioning what the
> source clock is...
>

Yes, we will document how t-high and t-low is derived from source.

>>> Wow, that's a cluster of arcane calls to handle a call that probably
>>> will never fail (it just enables clocks and sets pinctrl).  Sigh.
>>> ...but as far as I can tell the whole sequence is right.  You
>>> definitely need a "put" after a failed get and it looks like
>>> pm_runtime_set_suspended() has a special exception where it can be
>>> called if you got a runtime error...
>>
>> We didn't have this in before either. But this condition is somewhat
>> frequent if I2C transactions are called on cusp of exiting system suspend.
>> (e.g. PMIC slave getting a wakeup-IRQ and trying to read from PMIC through
>> I2C to read its status as to what caused that wake-up. At that time,
>> get_sync doesn't really enable resources (kernel 4.9) since the runtime-pm
>> ref-count isn't decremented. We run the risk of unclocked access if these
>> arcane calls aren't present. You can go through runtime-pm documentation
>> chapter 6 for more details.
> 
> Yeah, I certainly agree that the calls are needed if
> pm_runtime_get_sync() and I'm not suggesting removing them.  Hence the
> "as far as I can tell the whole sequence is right".
> 
> ...but I'm actually kinda worried if you're saying that you actually
> ran into this case.  Hopefully that got fixed and code no longer tries
> to read from the PMIC at a bad time anymore?  That code should be
> fixed not to be running so late in suspend.
> 

I have added Harry Y and Abhijeet D (developers for PMIC I2C client
team). They can comment if there is still a usecase of very late
transaction during suspend and/or very early transaction during resume.

> 
>>>>
>>>> +       /* Make sure no transactions are pending */
>>>> +       ret = i2c_trylock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
>>>> +       if (!ret) {
>>>> +               dev_err(gi2c->se.dev, "late I2C transaction request\n");
>>>> +               return -EBUSY;
>>>> +       }
>>>
>>>
>>> Does this happen?  How?
>>>
>>> Nothing about this code looks special for your hardware.  If this is
>>> really needed, why is it not part of the i2c core since there's
>>> nothing specific about your driver here?
>>>
>> There have been some clients that don't implement sys-suspend/resume
>> callbacks (so i2c adapter has no clue they are done with their transactions)
>> and this allows us to be flexible when they call I2C transactions extremely
>> late.
> 
> Still feels like this belongs in the i2c core, not your driver.  Maybe
> you should send a patch for the core and remove it from here?
> 
> ...and also, it seems like any i2c clients that don't implement the
> suspend/resume callbacks and try to do i2c transactions late in the
> game need to be fixed.  It should be documented that this isn't a
> valid thing for a driver to do and if we end up in this error case
> then it's not an i2c issue but it's a bad driver somewhere.
> 
You are right: this check is special for our HW due to usecases
mentioned above.
This check can go in i2c-core, but then it will not be necessary if
all adapters and clients that we work with are upstreamed (and all
implement system suspend/resume).
We will remove this in next version of geni i2c-adapter driver.

Thanks
Sagar

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Re: [v3, 3/4] i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller

[Karthik Ramasubramanian]

On 3/7/2018 2:16 PM, Doug Anderson wrote:
> Hi,
> 
> On Tue, Feb 27, 2018 at 5:38 PM, Karthikeyan Ramasubramanian
> <kramasub@codeaurora.org> wrote:
>> This bus driver supports the GENI based i2c hardware controller in the
>> Qualcomm SOCs. The Qualcomm Generic Interface (GENI) is a programmable
>> module supporting a wide range of serial interfaces including I2C. The
>> driver supports FIFO mode and DMA mode of transfer and switches modes
>> dynamically depending on the size of the transfer.
>>
>> Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
>> Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
>> Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>
>> ---
>>   drivers/i2c/busses/Kconfig         |  11 +
>>   drivers/i2c/busses/Makefile        |   1 +
>>   drivers/i2c/busses/i2c-qcom-geni.c | 626 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 638 insertions(+)
> 
> I'm not an expert on geni (and, to be honest, I haven't read the main
> geni patch yet).  ...but I figured I could at least add my $0.02 since
> I've stared at i2c bus drivers a lot in the past.  Feel free to tell
> me if I'm full or crap...
> 
> 
>>   create mode 100644 drivers/i2c/busses/i2c-qcom-geni.c
>>
>> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
>> index e2954fb..1ddf5cd 100644
>> --- a/drivers/i2c/busses/Kconfig
>> +++ b/drivers/i2c/busses/Kconfig
>> @@ -848,6 +848,17 @@ config I2C_PXA_SLAVE
>>            is necessary for systems where the PXA may be a target on the
>>            I2C bus.
>>
>> +config I2C_QCOM_GENI
>> +       tristate "Qualcomm Technologies Inc.'s GENI based I2C controller"
>> +       depends on ARCH_QCOM
>> +       depends on QCOM_GENI_SE
>> +       help
>> +         If you say yes to this option, support will be included for the
>> +         built-in I2C interface on the Qualcomm Technologies Inc.'s SoCs.
> 
> Kind of a generic description and this driver is only for new SoCs,
> right?  Maybe make it a little more specific?
Ok.
> 
> 
>> +
>> +         This driver can also be built as a module.  If so, the module
>> +         will be called i2c-qcom-geni.
>> +
>>   config I2C_QUP
>>          tristate "Qualcomm QUP based I2C controller"
>>          depends on ARCH_QCOM
>> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
>> index 2ce8576..201fce1 100644
>> --- a/drivers/i2c/busses/Makefile
>> +++ b/drivers/i2c/busses/Makefile
>> @@ -84,6 +84,7 @@ obj-$(CONFIG_I2C_PNX)         += i2c-pnx.o
>>   obj-$(CONFIG_I2C_PUV3)         += i2c-puv3.o
>>   obj-$(CONFIG_I2C_PXA)          += i2c-pxa.o
>>   obj-$(CONFIG_I2C_PXA_PCI)      += i2c-pxa-pci.o
>> +obj-$(CONFIG_I2C_QCOM_GENI)    += i2c-qcom-geni.o
>>   obj-$(CONFIG_I2C_QUP)          += i2c-qup.o
>>   obj-$(CONFIG_I2C_RIIC)         += i2c-riic.o
>>   obj-$(CONFIG_I2C_RK3X)         += i2c-rk3x.o
>> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
>> new file mode 100644
>> index 0000000..e1e4268
>> --- /dev/null
>> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
>> @@ -0,0 +1,626 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +// Copyright (c) 2017-2018, The Linux Foundation. All rights reserved.
>> +
>> +#include <linux/clk.h>
>> +#include <linux/dma-mapping.h>
>> +#include <linux/err.h>
>> +#include <linux/i2c.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/io.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/pm_runtime.h>
>> +#include <linux/qcom-geni-se.h>
>> +
>> +#define SE_I2C_TX_TRANS_LEN            0x26c
>> +#define SE_I2C_RX_TRANS_LEN            0x270
>> +#define SE_I2C_SCL_COUNTERS            0x278
>> +
>> +#define SE_I2C_ERR  (M_CMD_OVERRUN_EN | M_ILLEGAL_CMD_EN | M_CMD_FAILURE_EN |\
>> +                       M_GP_IRQ_1_EN | M_GP_IRQ_3_EN | M_GP_IRQ_4_EN)
>> +#define SE_I2C_ABORT           BIT(1)
>> +
>> +/* M_CMD OP codes for I2C */
>> +#define I2C_WRITE              0x1
>> +#define I2C_READ               0x2
>> +#define I2C_WRITE_READ         0x3
>> +#define I2C_ADDR_ONLY          0x4
>> +#define I2C_BUS_CLEAR          0x6
>> +#define I2C_STOP_ON_BUS                0x7
>> +/* M_CMD params for I2C */
>> +#define PRE_CMD_DELAY          BIT(0)
>> +#define TIMESTAMP_BEFORE       BIT(1)
>> +#define STOP_STRETCH           BIT(2)
>> +#define TIMESTAMP_AFTER                BIT(3)
>> +#define POST_COMMAND_DELAY     BIT(4)
>> +#define IGNORE_ADD_NACK                BIT(6)
>> +#define READ_FINISHED_WITH_ACK BIT(7)
>> +#define BYPASS_ADDR_PHASE      BIT(8)
>> +#define SLV_ADDR_MSK           GENMASK(15, 9)
>> +#define SLV_ADDR_SHFT          9
>> +/* I2C SCL COUNTER fields */
>> +#define HIGH_COUNTER_MSK       GENMASK(29, 20)
>> +#define HIGH_COUNTER_SHFT      20
>> +#define LOW_COUNTER_MSK                GENMASK(19, 10)
>> +#define LOW_COUNTER_SHFT       10
>> +#define CYCLE_COUNTER_MSK      GENMASK(9, 0)
>> +
>> +#define GP_IRQ0                        0
>> +#define GP_IRQ1                        1
>> +#define GP_IRQ2                        2
>> +#define GP_IRQ3                        3
>> +#define GP_IRQ4                        4
>> +#define GP_IRQ5                        5
>> +#define GENI_OVERRUN           6
>> +#define GENI_ILLEGAL_CMD       7
>> +#define GENI_ABORT_DONE                8
>> +#define GENI_TIMEOUT           9
> 
> Above should be an enum; then use the enum type as the parameter to
> geni_i2c_err() so it's obvious that "err" is not a normal linux error
> code.
> 
> 
>> +#define I2C_NACK               GP_IRQ1
>> +#define I2C_BUS_PROTO          GP_IRQ3
>> +#define I2C_ARB_LOST           GP_IRQ4
> 
> Get rid of definition of GP_IRQ1, 3, and 4 and just define I2C_NACK,
> I2C_BUS_PROTO, and I2C_ARB_LOST directly.
> 
> 
>> +#define DM_I2C_CB_ERR          ((BIT(GP_IRQ1) | BIT(GP_IRQ3) | BIT(GP_IRQ4)) \
>> +                                                                       << 5)
> 
> Should these really be using "GP_IRQ1", "GP_IRQ3", and "GP_IRQ4".
> Does this use of those numbers have anything to do with the other use
> of them?  Seems like this should just be BIT(1) | BIT(3) | BIT(4).
> 
> Said another way: does bit 1 in this field coorespond to NACK, bit 3
> correspond to BUS_PROTO, and bit 4 correspond to ARB_LOST?  If not
> then I see no reason to try to tie them together.  If they do
> correspond then use BIT(I2C_NACK), etc...
> 
The programming manual identifies the bits of the IRQ_STATUS register as 
GP_IRQ* and when the concerned serial engines are used as I2C 
controllers, those bit fields mean NACK, BUS_PROTO, ARB_LOST, etc. That 
is why it was mentioned that way. I will update as you point out.
> 
>> +
>> +#define I2C_AUTO_SUSPEND_DELAY 250
> 
> Why 250 ms?  That seems like an eternity.  Is it really that expensive
> to turn resources off and on?  I would sorta just expect clocks and
> stuff to get turned off right after a transaction finished unless
> another one was pending right behind it...
> 
> 
>> +#define KHz(freq)              (1000 * freq)
> 
> I probably wouldn't define KHz macro and just used numbers like 100000
> like all the other i2c drivers, but I guess it's OK.  Should be all
> caps, though?
I will change to all caps.
> 
> 
>> +#define PACKING_BYTES_PW       4
>> +
>> +struct geni_i2c_dev {
>> +       struct geni_se se;
>> +       u32 tx_wm;
>> +       int irq;
>> +       int err;
>> +       struct i2c_adapter adap;
>> +       struct completion done;
>> +       struct i2c_msg *cur;
>> +       int cur_wr;
>> +       int cur_rd;
>> +       u32 clk_freq_out;
>> +       const struct geni_i2c_clk_fld *clk_fld;
>> +};
>> +
>> +struct geni_i2c_err_log {
>> +       int err;
>> +       const char *msg;
>> +};
>> +
>> +static struct geni_i2c_err_log gi2c_log[] = {
> 
> static const?
Ok.
> 
> 
>> +       [GP_IRQ0] = {-EINVAL, "Unknown I2C err GP_IRQ0"},
>> +       [I2C_NACK] = {-ENOTCONN, "NACK: slv unresponsive, check its power/reset-ln"},
> 
> Longer than 80 characters; don't split the string, but you could still
> wrap better.
In the v2 patch, there was a comment to break the 80 character limit to 
improve the readability.
> 
> 
>> +       [GP_IRQ2] = {-EINVAL, "Unknown I2C err GP IRQ2"},
>> +       [I2C_BUS_PROTO] = {-EPROTO, "Bus proto err, noisy/unepxected start/stop"},
>> +       [I2C_ARB_LOST] = {-EBUSY, "Bus arbitration lost, clock line undriveable"},
>> +       [GP_IRQ5] = {-EINVAL, "Unknown I2C err GP IRQ5"},
>> +       [GENI_OVERRUN] = {-EIO, "Cmd overrun, check GENI cmd-state machine"},
>> +       [GENI_ILLEGAL_CMD] = {-EILSEQ, "Illegal cmd, check GENI cmd-state machine"},
>> +       [GENI_ABORT_DONE] = {-ETIMEDOUT, "Abort after timeout successful"},
>> +       [GENI_TIMEOUT] = {-ETIMEDOUT, "I2C TXN timed out"},
>> +};
>> +
>> +struct geni_i2c_clk_fld {
>> +       u32     clk_freq_out;
>> +       u8      clk_div;
>> +       u8      t_high;
>> +       u8      t_low;
>> +       u8      t_cycle;
>> +};
>> +
>> +static const struct geni_i2c_clk_fld geni_i2c_clk_map[] = {
>> +       {KHz(100), 7, 10, 11, 26},
>> +       {KHz(400), 2,  5, 12, 24},
>> +       {KHz(1000), 1, 3,  9, 18},
> 
> So I guess this is all relying on an input serial clock of 19.2MHz?
> Maybe document that?
> 
> Assuming I'm understanding the math here, is it really OK for your
> 100kHz and 1MHz mode to be running slightly fast?
> 
> 19200. / 2 / 24
>>>> 400.0
> 
> 19200. / 7 / 26
>>>> 105.49450549450549
> 
> 19200. / 1 / 18
>>>> 1066.6666666666667
> 
> It seems like you'd want the fastest clock that you can make that's
> _less than_ the spec.
> 
> 
> It would also be interesting to know if it's expected that boards
> might need to tweak the t_high / t_low depending on their electrical
> characteristics.  In the past I've had lots of requests from board
> makers to tweak things because they've got a long trace, or a stronger
> or weaker pull, or ...  If so we might later need to add some dts
> properties like "i2c-scl-rising-time-ns" and make the math more
> dynamic here, unless your hardware somehow automatically adjusts for
> this type of thing...
> 
> 
>> +};
>> +
>> +static int geni_i2c_clk_map_idx(struct geni_i2c_dev *gi2c)
>> +{
>> +       int i;
>> +       const struct geni_i2c_clk_fld *itr = geni_i2c_clk_map;
>> +
>> +       for (i = 0; i < ARRAY_SIZE(geni_i2c_clk_map); i++, itr++) {
>> +               if (itr->clk_freq_out == gi2c->clk_freq_out) {
>> +                       gi2c->clk_fld = geni_i2c_clk_map + i;
> 
> Isn't "geni_i2c_clk_map + i" just "itr"?
Yes right.
> 
> 
>> +                       return 0;
>> +               }
>> +       }
>> +       return -EINVAL;
>> +}
>> +
>> +static void qcom_geni_i2c_conf(struct geni_i2c_dev *gi2c)
>> +{
>> +       const struct geni_i2c_clk_fld *itr = gi2c->clk_fld;
>> +       u32 val;
>> +
>> +       writel_relaxed(0, gi2c->se.base + SE_GENI_CLK_SEL);
>> +
>> +       val = (itr->clk_div << CLK_DIV_SHFT) | SER_CLK_EN;
>> +       writel_relaxed(val, gi2c->se.base + GENI_SER_M_CLK_CFG);
>> +
>> +       val = itr->t_high << HIGH_COUNTER_SHFT;
>> +       val |= itr->t_low << LOW_COUNTER_SHFT;
>> +       val |= itr->t_cycle;
>> +       writel_relaxed(val, gi2c->se.base + SE_I2C_SCL_COUNTERS);
>> +       /*
>> +        * Ensure later writes/reads to serial engine register block is
>> +        * not reordered before this point.
>> +        */
>> +       mb();
> 
> This mb() is to make sure that later writes to "gi2c->se.base" are not
> reordered to be above the ones in this function?  You don't need a
> mb().  writel_relaxed() already enforces this.
Let me check if there are no readl_relaxed after this. If not, I will 
remove the barrier.
> 
> 
>> +}
>> +
>> +static void geni_i2c_err_misc(struct geni_i2c_dev *gi2c)
>> +{
>> +       u32 m_cmd = readl_relaxed(gi2c->se.base + SE_GENI_M_CMD0);
>> +       u32 m_stat = readl_relaxed(gi2c->se.base + SE_GENI_M_IRQ_STATUS);
>> +       u32 geni_s = readl_relaxed(gi2c->se.base + SE_GENI_STATUS);
>> +       u32 geni_ios = readl_relaxed(gi2c->se.base + SE_GENI_IOS);
>> +       u32 dma = readl_relaxed(gi2c->se.base + SE_GENI_DMA_MODE_EN);
>> +       u32 rx_st, tx_st;
>> +
>> +       if (dma) {
>> +               rx_st = readl_relaxed(gi2c->se.base + SE_DMA_RX_IRQ_STAT);
>> +               tx_st = readl_relaxed(gi2c->se.base + SE_DMA_TX_IRQ_STAT);
>> +       } else {
>> +               rx_st = readl_relaxed(gi2c->se.base + SE_GENI_RX_FIFO_STATUS);
>> +               tx_st = readl_relaxed(gi2c->se.base + SE_GENI_TX_FIFO_STATUS);
>> +       }
>> +       dev_dbg(gi2c->se.dev, "DMA:%d tx_stat:0x%x, rx_stat:0x%x, irq-stat:0x%x\n",
>> +               dma, tx_st, rx_st, m_stat);
>> +       dev_dbg(gi2c->se.dev, "m_cmd:0x%x, geni_status:0x%x, geni_ios:0x%x\n",
>> +               m_cmd, geni_s, geni_ios);
>> +}
>> +
>> +static void geni_i2c_err(struct geni_i2c_dev *gi2c, int err)
>> +{
>> +       gi2c->err = gi2c_log[err].err;
> 
> You should only set gi2c->err if it was 0 to start with.  You want
> "err" to contain the first error, not the last one.  This is
> especially important due to the comment elsewhere in this patch "if
> this is err with done-bit not set, handle that through timeout".  You
> don't want the timeout to clobber the true error.
True.
> 
> 
> On a separate note: I wonder if it makes sense to couch the rest of
> this function in something that will compile to a no-op if DEBUG and
> DYNAMIC_DEBUG aren't defined?  Then you can avoid including code for
> all these readl calls.
Given that these are not common scenarios, it may be a premature 
optimization.
> 
>> +       if (gi2c->cur)
>> +               dev_dbg(gi2c->se.dev, "len:%d, slv-addr:0x%x, RD/WR:%d\n",
>> +                       gi2c->cur->len, gi2c->cur->addr, gi2c->cur->flags);
>> +       dev_dbg(gi2c->se.dev, "%s\n", gi2c_log[err].msg);
>> +
>> +       if (err != I2C_NACK && err != GENI_ABORT_DONE)
>> +               geni_i2c_err_misc(gi2c);
>> +}
>> +
>> +static irqreturn_t geni_i2c_irq(int irq, void *dev)
>> +{
>> +       struct geni_i2c_dev *gi2c = dev;
>> +       int j;
>> +       u32 m_stat = readl_relaxed(gi2c->se.base + SE_GENI_M_IRQ_STATUS);
>> +       u32 rx_st = readl_relaxed(gi2c->se.base + SE_GENI_RX_FIFO_STATUS);
>> +       u32 dm_tx_st = readl_relaxed(gi2c->se.base + SE_DMA_TX_IRQ_STAT);
>> +       u32 dm_rx_st = readl_relaxed(gi2c->se.base + SE_DMA_RX_IRQ_STAT);
>> +       u32 dma = readl_relaxed(gi2c->se.base + SE_GENI_DMA_MODE_EN);
>> +       struct i2c_msg *cur = gi2c->cur;
>> +
>> +       if (!cur ||
>> +           m_stat & (M_CMD_FAILURE_EN | M_CMD_ABORT_EN) ||
>> +           dm_rx_st & (DM_I2C_CB_ERR)) {
>> +               if (m_stat & M_GP_IRQ_1_EN)
>> +                       geni_i2c_err(gi2c, I2C_NACK);
>> +               if (m_stat & M_GP_IRQ_3_EN)
>> +                       geni_i2c_err(gi2c, I2C_BUS_PROTO);
>> +               if (m_stat & M_GP_IRQ_4_EN)
>> +                       geni_i2c_err(gi2c, I2C_ARB_LOST);
>> +               if (m_stat & M_CMD_OVERRUN_EN)
>> +                       geni_i2c_err(gi2c, GENI_OVERRUN);
>> +               if (m_stat & M_ILLEGAL_CMD_EN)
>> +                       geni_i2c_err(gi2c, GENI_ILLEGAL_CMD);
>> +               if (m_stat & M_CMD_ABORT_EN)
>> +                       geni_i2c_err(gi2c, GENI_ABORT_DONE);
>> +               if (m_stat & M_GP_IRQ_0_EN)
>> +                       geni_i2c_err(gi2c, GP_IRQ0);
>> +
>> +               /* Disable the TX Watermark interrupt to stop TX */
>> +               if (!dma)
>> +                       writel_relaxed(0, gi2c->se.base +
>> +                                          SE_GENI_TX_WATERMARK_REG);
>> +               goto irqret;
>> +       }
>> +
>> +       if (dma) {
>> +               dev_dbg(gi2c->se.dev, "i2c dma tx:0x%x, dma rx:0x%x\n",
>> +                       dm_tx_st, dm_rx_st);
>> +               goto irqret;
>> +       }
>> +
>> +       if (cur->flags & I2C_M_RD &&
>> +           m_stat & (M_RX_FIFO_WATERMARK_EN | M_RX_FIFO_LAST_EN)) {
>> +               u32 rxcnt = rx_st & RX_FIFO_WC_MSK;
>> +
>> +               for (j = 0; j < rxcnt; j++) {
>> +                       u32 val;
>> +                       int p = 0;
>> +
>> +                       val = readl_relaxed(gi2c->se.base + SE_GENI_RX_FIFOn);
>> +                       while (gi2c->cur_rd < cur->len && p < sizeof(val)) {
>> +                               cur->buf[gi2c->cur_rd++] = val & 0xff;
>> +                               val >>= 8;
>> +                               p++;
>> +                       }
>> +                       if (gi2c->cur_rd == cur->len)
>> +                               break;
>> +               }
>> +       } else if (!(cur->flags & I2C_M_RD) &&
>> +                  m_stat & M_TX_FIFO_WATERMARK_EN) {
>> +               for (j = 0; j < gi2c->tx_wm; j++) {
>> +                       u32 temp;
>> +                       u32 val = 0;
>> +                       int p = 0;
>> +
>> +                       while (gi2c->cur_wr < cur->len && p < sizeof(val)) {
>> +                               temp = (u32)cur->buf[gi2c->cur_wr++];
> 
> What is the (u32) cast doing here?
The intention is to cast a char to u32. I will revisit its purpose and 
also check if any warnings were observed.
> 
> 
>> +                               val |= (temp << (p * 8));
> 
> Get rid of extra parenthesis.
Ok.
> 
> 
>> +                               p++;
>> +                       }
>> +                       writel_relaxed(val, gi2c->se.base + SE_GENI_TX_FIFOn);
>> +                       /* TX Complete, Disable the TX Watermark interrupt */
>> +                       if (gi2c->cur_wr == cur->len) {
>> +                               writel_relaxed(0, gi2c->se.base +
>> +                                               SE_GENI_TX_WATERMARK_REG);
>> +                               break;
>> +                       }
>> +               }
>> +       }
>> +irqret:
>> +       if (m_stat)
>> +               writel_relaxed(m_stat, gi2c->se.base + SE_GENI_M_IRQ_CLEAR);
>> +
>> +       if (dma) {
>> +               if (dm_tx_st)
>> +                       writel_relaxed(dm_tx_st, gi2c->se.base +
>> +                                               SE_DMA_TX_IRQ_CLR);
>> +               if (dm_rx_st)
>> +                       writel_relaxed(dm_rx_st, gi2c->se.base +
>> +                                               SE_DMA_RX_IRQ_CLR);
>> +       }
>> +       /* if this is err with done-bit not set, handle that through timeout. */
>> +       if (m_stat & M_CMD_DONE_EN)
>> +               complete(&gi2c->done);
>> +       else if ((dm_tx_st & TX_DMA_DONE) || (dm_rx_st & RX_DMA_DONE))
>> +               complete(&gi2c->done);
>> +
>> +       return IRQ_HANDLED;
>> +}
>> +
>> +static void geni_i2c_abort_xfer(struct geni_i2c_dev *gi2c)
>> +{
>> +       u32 val;
>> +       unsigned long timeout = HZ;
> 
> Rename to time_left?  ...and maybe use a #define for the init value?
Ok.
> 
> 
>> +
>> +       geni_i2c_err(gi2c, GENI_TIMEOUT);
>> +       gi2c->cur = NULL;
> 
> Don't you need a spinlock or something?  In most of the other cases
> you could get away with no locking because the irq isn't happening at
> the same time as other code that's mucking with stuff, but in the
> timeout case we may be mucking with stuff at the same time as the irq.
Except for aborting the current command, there is no yanking away of 
buffer used by IRQ. But I will check the programming manual regarding 
what will happen to the contents of the RX FIFO & access to the TX FIFO 
when the command gets aborted.
> 
> 
>> +       geni_se_abort_m_cmd(&gi2c->se);
>> +       do {
>> +               timeout = wait_for_completion_timeout(&gi2c->done, timeout);
>> +               val = readl_relaxed(gi2c->se.base + SE_GENI_M_IRQ_STATUS);
>> +       } while (!(val & M_CMD_ABORT_EN) && timeout);
> 
> Print an error if there was a timeout aborting?
Ok.
> 
> 
>> +}
>> +
>> +static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
>> +                               u32 m_param)
>> +{
>> +       dma_addr_t rx_dma;
>> +       enum geni_se_xfer_mode mode;
>> +       unsigned long timeout;
>> +
>> +       gi2c->cur = msg;
>> +       mode = msg->len > 32 ? GENI_SE_DMA : GENI_SE_FIFO;
> 
> DMA is hard and i2c transfers > 32 bytes are rare.  Do we really gain
> a lot by transferring i2c commands over DMA compared to a FIFO?
> Enough to justify the code complexity and the set of bugs that will
> show up?  I'm sure it will be a controversial assertion given that the
> code's already written, but personally I'd be supportive of ripping
> DMA mode out to simplify the driver.  I'd be curious if anyone else
> agrees.  To me it seems like premature optimization.
> 
> 
>> +       geni_se_select_mode(&gi2c->se, mode);
>> +       writel_relaxed(msg->len, gi2c->se.base + SE_I2C_RX_TRANS_LEN);
>> +       geni_se_setup_m_cmd(&gi2c->se, I2C_READ, m_param);
>> +       if (mode == GENI_SE_DMA) {
>> +               rx_dma = geni_se_rx_dma_prep(&gi2c->se, msg->buf, msg->len);
> 
> Randomly I noticed a flag called "I2C_M_DMA_SAFE".  Do we need to
> check this flag before using msg->buf for DMA?  ...or use
> i2c_get_dma_safe_msg_buf()?
> 
> ...btw: the relative lack of people doing this in the kernel is
> further evidence of DMA not really being worth it for i2c busses.
> 
> 
>> +               if (!rx_dma) {
>> +                       mode = GENI_SE_FIFO;
>> +                       geni_se_select_mode(&gi2c->se, mode);
>> +               }
>> +       }
>> +
>> +       timeout = wait_for_completion_timeout(&gi2c->done, HZ);
> 
> Perhaps make a #define for the timeout instead of just hardcoding HZ (1 second).
> 
> 
>> +       if (!timeout)
> 
> Can you rename "timeout" to "time_left"?  Otherwise this read like "if
> there wasn't a timeout then abort".
> 
> 
>> +               geni_i2c_abort_xfer(gi2c);
>> +
>> +       gi2c->cur_rd = 0;
>> +       if (mode == GENI_SE_DMA) {
>> +               if (gi2c->err) {
>> +                       writel_relaxed(1, gi2c->se.base + SE_DMA_RX_FSM_RST);
>> +                       wait_for_completion_timeout(&gi2c->done, HZ);
> 
> Worth printing an error if this one times out?  Seems like we'd be in
> bad shape...
Ok.
> 
> ...also: to be paranoid do you need a re_init_completion before you
> reset things?  In theory one could conceive of the concept that the
> earlier completion timed out and then the DMA interrupt came right
> after.  Now there will be a completion already on the books so your
> wait will return instantly even though the reset hasn't been done.
> 
reinit_completion can help only if the prior DMA interrupt came before 
reinit_completion. If it comes after reinit_completion, then it will end 
up signaling the wait prematurely.

Rather the better idea is to wait and check if indeed the reset is done. 
If it is done, then all is fine. Else go back to wait again. Same logic 
like in the case of abort.
> 
>> +               }
>> +               geni_se_rx_dma_unprep(&gi2c->se, rx_dma, msg->len);
>> +       }
>> +       if (gi2c->err)
>> +               dev_err(gi2c->se.dev, "i2c error :%d\n", gi2c->err);
> 
> OK, so I'm a bit baffled.  You've got all these tables in this driver
> that give you nice/informative error messages.  Then those nice error
> messages are just calling dev_dbg() and here you print out an arcane
> linux error?
Agree, I will try to log a human-readable error while avoiding the log spew.
> 
> Also: seems like you wouldn't want to print errors for NACKs, right?
> Otherwise i2cdetect is going to be spewing isn't it?
> 
> 
>> +       return gi2c->err;
>> +}
>> +
>> +static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
>> +                               u32 m_param)
>> +{
>> +       dma_addr_t tx_dma;
>> +       enum geni_se_xfer_mode mode;
>> +       unsigned long timeout;
>> +
>> +       gi2c->cur = msg;
>> +       mode = msg->len > 32 ? GENI_SE_DMA : GENI_SE_FIFO;
>> +       geni_se_select_mode(&gi2c->se, mode);
>> +       writel_relaxed(msg->len, gi2c->se.base + SE_I2C_TX_TRANS_LEN);
>> +       geni_se_setup_m_cmd(&gi2c->se, I2C_WRITE, m_param);
>> +       if (mode == GENI_SE_DMA) {
>> +               tx_dma = geni_se_tx_dma_prep(&gi2c->se, msg->buf, msg->len);
>> +               if (!tx_dma) {
>> +                       mode = GENI_SE_FIFO;
>> +                       geni_se_select_mode(&gi2c->se, mode);
>> +               }
>> +       }
>> +
>> +       if (mode == GENI_SE_FIFO) /* Get FIFO IRQ */
>> +               writel_relaxed(1, gi2c->se.base + SE_GENI_TX_WATERMARK_REG);
>> +
>> +       timeout = wait_for_completion_timeout(&gi2c->done, HZ);
>> +       if (!timeout)
>> +               geni_i2c_abort_xfer(gi2c);
>> +
>> +       gi2c->cur_wr = 0;
>> +       if (mode == GENI_SE_DMA) {
>> +               if (gi2c->err) {
>> +                       writel_relaxed(1, gi2c->se.base + SE_DMA_TX_FSM_RST);
>> +                       wait_for_completion_timeout(&gi2c->done, HZ);
>> +               }
>> +               geni_se_tx_dma_unprep(&gi2c->se, tx_dma, msg->len);
>> +       }
>> +       if (gi2c->err)
>> +               dev_err(gi2c->se.dev, "i2c error :%d\n", gi2c->err);
>> +       return gi2c->err;
>> +}
>> +
>> +static int geni_i2c_xfer(struct i2c_adapter *adap,
>> +                        struct i2c_msg msgs[],
>> +                        int num)
>> +{
>> +       struct geni_i2c_dev *gi2c = i2c_get_adapdata(adap);
>> +       int i, ret;
>> +
>> +       gi2c->err = 0;
>> +       reinit_completion(&gi2c->done);
>> +       ret = pm_runtime_get_sync(gi2c->se.dev);
>> +       if (ret < 0) {
>> +               dev_err(gi2c->se.dev, "error turning SE resources:%d\n", ret);
>> +               pm_runtime_put_noidle(gi2c->se.dev);
>> +               /* Set device in suspended since resume failed */
>> +               pm_runtime_set_suspended(gi2c->se.dev);
>> +               return ret;
> 
> Wow, that's a cluster of arcane calls to handle a call that probably
> will never fail (it just enables clocks and sets pinctrl).  Sigh.
> ...but as far as I can tell the whole sequence is right.  You
> definitely need a "put" after a failed get and it looks like
> pm_runtime_set_suspended() has a special exception where it can be
> called if you got a runtime error...
> 
> 
>> +       }
>> +
>> +       qcom_geni_i2c_conf(gi2c);
>> +       for (i = 0; i < num; i++) {
>> +               u32 m_param = i < (num - 1) ? STOP_STRETCH : 0;
>> +
>> +               m_param |= ((msgs[i].addr << SLV_ADDR_SHFT) & SLV_ADDR_MSK);
>> +
>> +               if (msgs[i].flags & I2C_M_RD)
>> +                       ret = geni_i2c_rx_one_msg(gi2c, &msgs[i], m_param);
>> +               else
>> +                       ret = geni_i2c_tx_one_msg(gi2c, &msgs[i], m_param);
>> +
>> +               if (ret) {
>> +                       dev_err(gi2c->se.dev, "i2c error %d @ %d\n", ret, i);
>> +                       break;
>> +               }
>> +       }
>> +       if (ret == 0)
>> +               ret = num;
>> +
>> +       pm_runtime_mark_last_busy(gi2c->se.dev);
>> +       pm_runtime_put_autosuspend(gi2c->se.dev);
>> +       gi2c->cur = NULL;
>> +       gi2c->err = 0;
>> +       return ret;
>> +}
>> +
>> +static u32 geni_i2c_func(struct i2c_adapter *adap)
>> +{
>> +       return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
>> +}
>> +
>> +static const struct i2c_algorithm geni_i2c_algo = {
>> +       .master_xfer    = geni_i2c_xfer,
>> +       .functionality  = geni_i2c_func,
>> +};
>> +
>> +static int geni_i2c_probe(struct platform_device *pdev)
>> +{
>> +       struct geni_i2c_dev *gi2c;
>> +       struct resource *res;
>> +       u32 proto, tx_depth;
>> +       int ret;
>> +
>> +       gi2c = devm_kzalloc(&pdev->dev, sizeof(*gi2c), GFP_KERNEL);
>> +       if (!gi2c)
>> +               return -ENOMEM;
>> +
>> +       gi2c->se.dev = &pdev->dev;
>> +       gi2c->se.wrapper = dev_get_drvdata(pdev->dev.parent);
>> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> +       gi2c->se.base = devm_ioremap_resource(&pdev->dev, res);
>> +       if (IS_ERR(gi2c->se.base)) {
>> +               ret = PTR_ERR(gi2c->se.base);
>> +               dev_err(&pdev->dev, "Err IO Mapping register block %d\n", ret);
> 
> No need for error message with devm_ioremap_resource().
Ok.
> 
> 
>> +               return ret;
>> +       }
>> +
>> +       gi2c->se.clk = devm_clk_get(&pdev->dev, "se");
>> +       if (IS_ERR(gi2c->se.clk)) {
>> +               ret = PTR_ERR(gi2c->se.clk);
>> +               dev_err(&pdev->dev, "Err getting SE Core clk %d\n", ret);
>> +               return ret;
>> +       }
>> +
>> +       ret = device_property_read_u32(&pdev->dev, "clock-frequency",
>> +                                                       &gi2c->clk_freq_out);
>> +       if (ret) {
>> +               dev_info(&pdev->dev,
>> +                       "Bus frequency not specified, default to 400KHz.\n");
>> +               gi2c->clk_freq_out = KHz(400);
>> +       }
> 
> I feel like it should default to 100KHz.  i2c_parse_fw_timings()
> defaults to this and to me the wording "New drivers almost always
> should use the defaults" makes me feel this should be the defaults.
> 
>> +
>> +       gi2c->irq = platform_get_irq(pdev, 0);
>> +       if (gi2c->irq < 0) {
>> +               dev_err(&pdev->dev, "IRQ error for i2c-geni\n");
>> +               return gi2c->irq;
>> +       }
>> +
>> +       ret = geni_i2c_clk_map_idx(gi2c);
>> +       if (ret) {
>> +               dev_err(&pdev->dev, "Invalid clk frequency %d KHz: %d\n",
>> +                       gi2c->clk_freq_out, ret);
> 
> Need a divide by 1000 since your printout includes "KHz".  Also note
> that the proper Si units is kHz not KHz, isn't it?
I will remove the KHz and just log as Hz.
> 
> 
>> +               return ret;
>> +       }
>> +
>> +       gi2c->adap.algo = &geni_i2c_algo;
>> +       init_completion(&gi2c->done);
>> +       platform_set_drvdata(pdev, gi2c);
>> +       ret = devm_request_irq(&pdev->dev, gi2c->irq, geni_i2c_irq,
>> +                              IRQF_TRIGGER_HIGH, "i2c_geni", gi2c);
>> +       if (ret) {
>> +               dev_err(&pdev->dev, "Request_irq failed:%d: err:%d\n",
>> +                       gi2c->irq, ret);
>> +               return ret;
>> +       }
>> +       disable_irq(gi2c->irq);
> 
> Can you explain the goal of the disable_irq() here.  Is it actually
> needed for something or does it somehow save power?  From drivers I've
> reviewed in the past this doesn't seem like a common thing to do, so
> I'm curious what it's supposed to gain for you.  I'd be inclined to
> just delete the whole disable/enable of the irq from this driver.
> 
> 
>> +       i2c_set_adapdata(&gi2c->adap, gi2c);
>> +       gi2c->adap.dev.parent = &pdev->dev;
>> +       gi2c->adap.dev.of_node = pdev->dev.of_node;
>> +       strlcpy(gi2c->adap.name, "Geni-I2C", sizeof(gi2c->adap.name));
>> +
>> +       ret = geni_se_resources_on(&gi2c->se);
>> +       if (ret) {
>> +               dev_err(&pdev->dev, "Error turning on resources %d\n", ret);
>> +               return ret;
>> +       }
>> +       proto = geni_se_read_proto(&gi2c->se);
>> +       tx_depth = geni_se_get_tx_fifo_depth(&gi2c->se);
>> +       if (unlikely(proto != GENI_SE_I2C)) {
> 
> Avoid compiler hints like unlikely() unless you're really truly
> optimizing a tight inner loop.  Otherwise let the compiler do its job.
Ok.
> 
> 
>> +               dev_err(&pdev->dev, "Invalid proto %d\n", proto);
>> +               geni_se_resources_off(&gi2c->se);
>> +               return -ENXIO;
>> +       }
>> +       gi2c->tx_wm = tx_depth - 1;
>> +       geni_se_init(&gi2c->se, gi2c->tx_wm, tx_depth);
>> +       geni_se_config_packing(&gi2c->se, BITS_PER_BYTE, PACKING_BYTES_PW,
>> +                                                       true, true, true);
>> +       geni_se_resources_off(&gi2c->se);
>> +       dev_dbg(&pdev->dev, "i2c fifo/se-dma mode. fifo depth:%d\n", tx_depth);
>> +
>> +       pm_runtime_set_suspended(gi2c->se.dev);
>> +       pm_runtime_set_autosuspend_delay(gi2c->se.dev, I2C_AUTO_SUSPEND_DELAY);
>> +       pm_runtime_use_autosuspend(gi2c->se.dev);
>> +       pm_runtime_enable(gi2c->se.dev);
>> +       i2c_add_adapter(&gi2c->adap);
>> +
>> +       dev_dbg(&pdev->dev, "I2C probed\n");
> 
> Is this really a useful dev_dbg()?  Just turn on initcall debugging...
Can be removed.
> 
> 
>> +       return 0;
>> +}
>> +
>> +static int geni_i2c_remove(struct platform_device *pdev)
>> +{
>> +       struct geni_i2c_dev *gi2c = platform_get_drvdata(pdev);
>> +
>> +       pm_runtime_disable(gi2c->se.dev);
> 
> Is this right?  You don't want to disable PM Runtime transitions but
> you actually want to force the adapter into suspended state, don't
> you?  I don't see anything that does that...
> 
> 
>> +       i2c_del_adapter(&gi2c->adap);
>> +       return 0;
>> +}
>> +
>> +static int geni_i2c_resume_noirq(struct device *device)
>> +{
>> +       return 0;
>> +}
> 
> No need for a dummy function; just stick NULL in the structure, no?
> 
>> +
>> +#ifdef CONFIG_PM
>> +static int geni_i2c_runtime_suspend(struct device *dev)
>> +{
>> +       struct geni_i2c_dev *gi2c = dev_get_drvdata(dev);
>> +
>> +       disable_irq(gi2c->irq);
>> +       geni_se_resources_off(&gi2c->se);
>> +       return 0;
>> +}
>> +
>> +static int geni_i2c_runtime_resume(struct device *dev)
>> +{
>> +       int ret;
>> +       struct geni_i2c_dev *gi2c = dev_get_drvdata(dev);
>> +
>> +       ret = geni_se_resources_on(&gi2c->se);
>> +       if (ret)
>> +               return ret;
>> +
>> +       enable_irq(gi2c->irq);
>> +       return 0;
>> +}
>> +
>> +static int geni_i2c_suspend_noirq(struct device *device)
>> +{
>> +       struct geni_i2c_dev *gi2c = dev_get_drvdata(device);
>> +       int ret;
>> +
>> +       /* Make sure no transactions are pending */
>> +       ret = i2c_trylock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
>> +       if (!ret) {
>> +               dev_err(gi2c->se.dev, "late I2C transaction request\n");
>> +               return -EBUSY;
>> +       }
> 
> Does this happen?  How?
> 
> Nothing about this code looks special for your hardware.  If this is
> really needed, why is it not part of the i2c core since there's
> nothing specific about your driver here?
> 
> 
>> +       if (!pm_runtime_status_suspended(device)) {
>> +               geni_i2c_runtime_suspend(device);
>> +               pm_runtime_disable(device);
>> +               pm_runtime_set_suspended(device);
>> +               pm_runtime_enable(device);
>> +       }
> 
> Similar question.  Why do you need this special case code?  Are there
> cases where we're all the way at suspend_noirq and yet we still
> haven't runtime suspended?  Can you please document how we get into
> this state?
> 
> 
>> +       i2c_unlock_bus(&gi2c->adap, I2C_LOCK_SEGMENT);
>> +       return 0;
>> +}
>> +#else
>> +static int geni_i2c_runtime_suspend(struct device *dev)
>> +{
>> +       return 0;
>> +}
>> +
>> +static int geni_i2c_runtime_resume(struct device *dev)
>> +{
>> +       return 0;
>> +}
>> +
>> +static int geni_i2c_suspend_noirq(struct device *device)
>> +{
>> +       return 0;
>> +}
>> +#endif
>> +
>> +static const struct dev_pm_ops geni_i2c_pm_ops = {
>> +       .suspend_noirq          = geni_i2c_suspend_noirq,
>> +       .resume_noirq           = geni_i2c_resume_noirq,
>> +       .runtime_suspend        = geni_i2c_runtime_suspend,
>> +       .runtime_resume         = geni_i2c_runtime_resume,
> 
> Please use SET_NOIRQ_SYSTEM_SLEEP_PM_OPS and SET_RUNTIME_PM_OPS.  Then
> you can get rid of all the dummy functions.  AKA something like:
> 
> static const struct dev_pm_ops geni_i2c_pm_ops = {
>    SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(geni_i2c_suspend_noirq, NULL)
>    SET_RUNTIME_PM_OPS(geni_i2c_runtime_suspend, geni_i2c_runtime_resume, NULL)
> };
> 
Ok.
> 
>> +};
>> +
>> +static const struct of_device_id geni_i2c_dt_match[] = {
>> +       { .compatible = "qcom,geni-i2c" },
>> +       {}
>> +};
>> +MODULE_DEVICE_TABLE(of, geni_i2c_dt_match);
>> +
>> +static struct platform_driver geni_i2c_driver = {
>> +       .probe  = geni_i2c_probe,
>> +       .remove = geni_i2c_remove,
>> +       .driver = {
>> +               .name = "geni_i2c",
>> +               .pm = &geni_i2c_pm_ops,
>> +               .of_match_table = geni_i2c_dt_match,
>> +       },
>> +};
>> +
>> +module_platform_driver(geni_i2c_driver);
>> +
>> +MODULE_DESCRIPTION("I2C Controller Driver for GENI based QUP cores");
>> +MODULE_LICENSE("GPL v2");

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