Re: [PATCH i2c-next v9 5/5] i2c: aspeed: Add bus idle waiting logic for multi-master use cases

Wolfram Sang
2018-11-28T21:54:46Z

On Tue, Oct 30, 2018 at 02:09:16PM -0700, Jae Hyun Yoo wrote:
> In multi-master environment, this driver's master cannot know
> exactly when a peer master sends data to this driver's slave so a
> case can be happened that this master tries to send data through
> the master_xfer function but slave data from peer master is still
> being processed by this driver.

So, that I get this correct: your IP core cannot detect a bus busy state
when its own slave address is acessed? Well, I know HW can have bugs,
but I still wonder because a bus is busy as soon as another START has
been detected, independent of which device is going to be accessed.

Even if so, why can't you use a mutex to prevent any master_xfer while
slave_xfer is ongoing?

Shouldn't that be enough according to the above description? Why do you
need the delay? I might be missing something...

> To prevent any state corruption in the case, this patch adds
> checking code if any slave operation is ongoing and it waits up to
> the bus timeout duration before starting a master_xfer operation.
>
> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
> Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
> ---
> drivers/i2c/busses/i2c-aspeed.c | 55 ++++++++++++++++++++++++---------
> 1 file changed, 40 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index 833b6b6a4c7e..30c3ab3a4844 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -12,6 +12,7 @@
>
> #include <linux/clk.h>
> #include <linux/completion.h>
> +#include <linux/delay.h>
> #include <linux/err.h>
> #include <linux/errno.h>
> #include <linux/i2c.h>
> @@ -115,6 +116,9 @@
> /* 0x18 : I2CD Slave Device Address Register */
> #define ASPEED_I2CD_DEV_ADDR_MASK GENMASK(6, 0)
>
> +/* Busy checking */
> +#define ASPEED_I2C_BUS_BUSY_CHECK_INTERVAL_US (10 * 1000)
> +
> enum aspeed_i2c_master_state {
> ASPEED_I2C_MASTER_INACTIVE,
> ASPEED_I2C_MASTER_START,
> @@ -156,6 +160,8 @@ struct aspeed_i2c_bus {
> int cmd_err;
> /* Protected only by i2c_lock_bus */
> int master_xfer_result;
> + /* Multi-master */
> + bool multi_master;
> #if IS_ENABLED(CONFIG_I2C_SLAVE)
> struct i2c_client *slave;
> enum aspeed_i2c_slave_state slave_state;
> @@ -596,27 +602,44 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
> return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
> }
>
> +static int aspeed_i2c_check_bus_busy(struct aspeed_i2c_bus *bus)
> +{
> + unsigned long timeout;
> +
> + if (bus->multi_master) {
> + might_sleep();
> + /* Initialize it only when multi_master is set */
> + timeout = jiffies + bus->adap.timeout;
> + }
> +
> + for (;;) {
> + if (!(readl(bus->base + ASPEED_I2C_CMD_REG) &
> + ASPEED_I2CD_BUS_BUSY_STS))
> +#if IS_ENABLED(CONFIG_I2C_SLAVE)
> + if (bus->slave_state == ASPEED_I2C_SLAVE_STOP)
> +#endif
> + return 0;
> + if (!bus->multi_master)
> + break;
> + if (time_after(jiffies, timeout))
> + break;
> + usleep_range((ASPEED_I2C_BUS_BUSY_CHECK_INTERVAL_US >> 2) + 1,
> + ASPEED_I2C_BUS_BUSY_CHECK_INTERVAL_US);
> + }
> +
> + return aspeed_i2c_recover_bus(bus);
> +}
> +
> static int aspeed_i2c_master_xfer(struct i2c_adapter *adap,
> struct i2c_msg *msgs, int num)
> {
> struct aspeed_i2c_bus *bus = i2c_get_adapdata(adap);
> unsigned long time_left, flags;
> - int ret = 0;
>
> - spin_lock_irqsave(&bus->lock, flags);
> - bus->cmd_err = 0;
> -
> - /* If bus is busy, attempt recovery. We assume a single master
> - * environment.
> - */
> - if (readl(bus->base + ASPEED_I2C_CMD_REG) & ASPEED_I2CD_BUS_BUSY_STS) {
> - spin_unlock_irqrestore(&bus->lock, flags);
> - ret = aspeed_i2c_recover_bus(bus);
> - if (ret)
> - return ret;
> - spin_lock_irqsave(&bus->lock, flags);
> - }
> + if (aspeed_i2c_check_bus_busy(bus))
> + return -EAGAIN;
>
> + spin_lock_irqsave(&bus->lock, flags);
> bus->cmd_err = 0;
> bus->msgs = msgs;
> bus->msgs_index = 0;
> @@ -827,7 +850,9 @@ static int aspeed_i2c_init(struct aspeed_i2c_bus *bus,
> if (ret < 0)
> return ret;
>
> - if (!of_property_read_bool(pdev->dev.of_node, "multi-master"))
> + if (of_property_read_bool(pdev->dev.of_node, "multi-master"))
> + bus->multi_master = true;
> + else
> fun_ctrl_reg |= ASPEED_I2CD_MULTI_MASTER_DIS;
>
> /* Enable Master Mode */
> --
> 2.19.1
>