Re: [PATCH v4 3/5] i2c:ocores: add polling interface

Peter Rosin
2019-02-11T10:43:45Z

On 2019-02-11 09:31, Federico Vaga wrote:
> This driver assumes that an interrupt line is always available for
> the I2C master. This is not always the case and this patch adds support
> for a polling version.
>
> Report from Andrew Lunn:
>
> I did some timing tests for this. On my box, we request a udelay of
> 80uS. The kernel actually delays for about 79uS. We then spin in
> ocores_wait() for an additional 10-11uS, which is 3 to 4 iterations.
>
> There are actually 9 bits on the wire, not 8, since there is an
> ACK/NACK bit after the actual data transfer. So i changed the delay to
> (9 * 1000) / i2c->bus_clock_khz. That resulted in ocores_wait() mostly
> not looping at all. But for reading an 4K AT24 EEPROM, it increased
> the read time by 10ms, from 424ms to 434ms. So we should probably keep
> with 8.
>
> Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
> Tested-by: Andrew Lunn <andrew@lunn.ch>
>
> ---
> drivers/i2c/busses/i2c-ocores.c | 180 +++++++++++++++++++++++++++++++++++-----
> 1 file changed, 160 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-ocores.c b/drivers/i2c/busses/i2c-ocores.c
> index fcc2558..d42a324 100644
> --- a/drivers/i2c/busses/i2c-ocores.c
> +++ b/drivers/i2c/busses/i2c-ocores.c
> @@ -13,6 +13,7 @@
> */
>
> #include <linux/clk.h>
> +#include <linux/delay.h>
> #include <linux/err.h>
> #include <linux/kernel.h>
> #include <linux/module.h>
> @@ -26,6 +27,9 @@
> #include <linux/io.h>
> #include <linux/log2.h>
> #include <linux/spinlock.h>
> +#include <linux/jiffies.h>
> +
> +#define OCORES_FLAG_POLL BIT(0)
>
> /**
> * @process_lock: protect I2C transfer process.
> @@ -35,6 +39,7 @@ struct ocores_i2c {
> void __iomem *base;
> u32 reg_shift;
> u32 reg_io_width;
> + unsigned long flags;
> wait_queue_head_t wait;
> struct i2c_adapter adap;
> struct i2c_msg *msg;
> @@ -246,10 +251,117 @@ static void ocores_process_timeout(struct ocores_i2c *i2c)
> spin_unlock_irqrestore(&i2c->process_lock, flags);
> }
>
> -static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> +/**
> + * Wait until something change in a given register
> + * @i2c: ocores I2C device instance
> + * @reg: register to query
> + * @mask: bitmask to apply on register value
> + * @val: expected result
> + * @timeout: timeout in jiffies
> + *
> + * Timeout is necessary to avoid to stay here forever when the chip
> + * does not answer correctly.
> + *
> + * Return: 0 on success, -ETIMEDOUT on timeout
> + */
> +static int ocores_wait(struct ocores_i2c *i2c,
> + int reg, u8 mask, u8 val,
> + const unsigned long timeout)
> +{
> + unsigned long j;
> +
> + j = jiffies + timeout;
> + while (1) {
> + u8 status = oc_getreg(i2c, reg);
> +
> + if ((status & mask) == val)
> + break;
> +
> + if (time_after(jiffies, j))
> + return -ETIMEDOUT;
> + }
> + return 0;
> +}
> +
> +/**
> + * Wait until is possible to process some data
> + * @i2c: ocores I2C device instance
> + *
> + * Used when the device is in polling mode (interrupts disabled).
> + *
> + * Return: 0 on success, -ETIMEDOUT on timeout
> + */
> +static int ocores_poll_wait(struct ocores_i2c *i2c)
> +{
> + u8 mask;
> + int err;
> +
> + if (i2c->state == STATE_DONE || i2c->state == STATE_ERROR) {
> + /* transfer is over */
> + mask = OCI2C_STAT_BUSY;
> + } else {
> + /* on going transfer */
> + mask = OCI2C_STAT_TIP;
> + /*
> + * We wait for the data to be transfered (8bit),
> + * then we start polling on the ACK/NACK bit
> + */
> + udelay((8 * 1000) / i2c->bus_clock_khz);
> + }
> +
> + /*
> + * once we are here we expect to get the expected result immediately
> + * so if after 1ms we timeout then something is broken.
> + */
> + err = ocores_wait(i2c, OCI2C_STATUS, mask, 0, msecs_to_jiffies(1));
> + if (err)
> + dev_warn(i2c->adap.dev.parent,
> + "%s: STATUS timeout, bit 0x%x did not clear in 1ms\n",
> + __func__, mask);
> + return err;
> +}
> +
> +
> +/**
> + * It handles an IRQ-less transfer
> + * @i2c: ocores I2C device instance
> + *
> + * Even if IRQ are disabled, the I2C OpenCore IP behavior is exactly the same
> + * (only that IRQ are not produced). This means that we can re-use entirely
> + * ocores_isr(), we just add our polling code around it.
> + *
> + * It can run in atomic context
> + */
> +static void ocores_process_polling(struct ocores_i2c *i2c)
> +{
> + while (1) {
> + irqreturn_t ret;
> + int err;
> +
> + err = ocores_poll_wait(i2c);
> + if (err) {
> + i2c->state = STATE_ERROR;
> + break; /* timeout */
> + }
> +
> + ret = ocores_isr(-1, i2c);
> + if (ret == IRQ_NONE)
> + break; /* all messages have been transfered */
> + }
> +}
> +
> +static int ocores_xfer_core(struct ocores_i2c *i2c,
> + struct i2c_msg *msgs, int num,
> + bool polling)
> {
> - struct ocores_i2c *i2c = i2c_get_adapdata(adap);
> int ret;
> + u8 ctrl;
> +
> + ctrl = oc_getreg(i2c, OCI2C_CONTROL);
> + if (polling)
> + oc_setreg(i2c, OCI2C_CONTROL, ctrl & ~OCI2C_CTRL_IEN);
> + else
> + oc_setreg(i2c, OCI2C_CONTROL, ctrl | OCI2C_CTRL_IEN);
>
> i2c->msg = msgs;
> i2c->pos = 0;
> @@ -259,16 +371,37 @@ static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> oc_setreg(i2c, OCI2C_DATA, i2c_8bit_addr_from_msg(i2c->msg));
> oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
>
> - ret = wait_event_timeout(i2c->wait, (i2c->state == STATE_ERROR) ||
> - (i2c->state == STATE_DONE), HZ);
> - if (ret == 0) {
> - ocores_process_timeout(i2c);
> - return -ETIMEDOUT;
> + if (polling) {
> + ocores_process_polling(i2c);
> + } else {
> + ret = wait_event_timeout(i2c->wait,
> + (i2c->state == STATE_ERROR) ||
> + (i2c->state == STATE_DONE), HZ);
> + if (ret == 0) {
> + ocores_process_timeout(i2c);
> + return -ETIMEDOUT;
> + }
> }
>
> return (i2c->state == STATE_DONE) ? num : -EIO;
> }
>
> +static int ocores_xfer_polling(struct i2c_adapter *adap,
> + struct i2c_msg *msgs, int num)
> +{
> + return ocores_xfer_core(i2c_get_adapdata(adap), msgs, num, true);
> +}
> +
> +static int ocores_xfer(struct i2c_adapter *adap,
> + struct i2c_msg *msgs, int num)
> +{
> + struct ocores_i2c *i2c = i2c_get_adapdata(adap);
> +
> + if (i2c->flags & OCORES_FLAG_POLL)
> + return ocores_xfer_polling(adap, msgs, num);
> + return ocores_xfer_core(i2c, msgs, num, false);
> +}
> +
> static int ocores_init(struct device *dev, struct ocores_i2c *i2c)
> {
> int prescale;
> @@ -294,7 +427,7 @@ static int ocores_init(struct device *dev, struct ocores_i2c *i2c)
>
> /* Init the device */
> oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_IACK);
> - oc_setreg(i2c, OCI2C_CONTROL, ctrl | OCI2C_CTRL_IEN | OCI2C_CTRL_EN);
> + oc_setreg(i2c, OCI2C_CONTROL, ctrl | OCI2C_CTRL_EN);

You fix this up in patch 5 (in what is perhaps carelessly marketed as
fixes for minor checkpatch issues), but for this patch you are actually
no longer making sure that you clear the OCI2C_CTRL_IEN bit as the code
used to before this patch. I think you intended to preserve that
behavior, no?

Cheers,
Peter

>
> return 0;
> }
> @@ -451,10 +584,6 @@ static int ocores_i2c_probe(struct platform_device *pdev)
> int ret;
> int i;
>
> - irq = platform_get_irq(pdev, 0);
> - if (irq < 0)
> - return irq;
> -
> i2c = devm_kzalloc(&pdev->dev, sizeof(*i2c), GFP_KERNEL);
> if (!i2c)
> return -ENOMEM;
> @@ -509,18 +638,29 @@ static int ocores_i2c_probe(struct platform_device *pdev)
> }
> }
>
> + init_waitqueue_head(&i2c->wait);
> +
> + irq = platform_get_irq(pdev, 0);
> + if (irq == -ENXIO) {
> + i2c->flags |= OCORES_FLAG_POLL;
> + } else {
> + if (irq < 0)
> + return irq;
> + }
> +
> + if (!(i2c->flags & OCORES_FLAG_POLL)) {
> + ret = devm_request_irq(&pdev->dev, irq, ocores_isr, 0,
> + pdev->name, i2c);
> + if (ret) {
> + dev_err(&pdev->dev, "Cannot claim IRQ\n");
> + goto err_clk;
> + }
> + }
> +
> ret = ocores_init(&pdev->dev, i2c);
> if (ret)
> goto err_clk;
>
> - init_waitqueue_head(&i2c->wait);
> - ret = devm_request_irq(&pdev->dev, irq, ocores_isr, 0,
> - pdev->name, i2c);
> - if (ret) {
> - dev_err(&pdev->dev, "Cannot claim IRQ\n");
> - goto err_clk;
> - }
> -
> /* hook up driver to tree */
> platform_set_drvdata(pdev, i2c);
> i2c->adap = ocores_adapter;
>