v6->v7: 1. some dirty patches were removed 2. rename structure member 'to/ti' to 't1/t2' to make it easier to understand. 3. add a comment about arbitration. Link: https://lore.kernel.org/all/b0f284621b6763c32133d39be83f05f1184b3635.1703830854.git.hanshu-oc@xxxxxxxxxxx/ During each byte access, the host performs clock stretching. In this case, the thread may be interrupted by preemption, resulting in a long stretching time. However, some touchpad can only tolerate host clock stretching of no more than 200 ms. We reduce the impact of this through a retransmission mechanism. Since __i2c_lock_bus_helper() is used to ensure that the current access will not be interrupted by the other access, We don't need to worry about arbitration anymore. Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxx> Signed-off-by: Hans Hu <hanshu-oc@xxxxxxxxxxx> --- drivers/i2c/busses/i2c-viai2c-common.c | 26 ++++++++++++++++++++++++++ drivers/i2c/busses/i2c-viai2c-common.h | 3 +++ 2 files changed, 29 insertions(+) diff --git a/drivers/i2c/busses/i2c-viai2c-common.c b/drivers/i2c/busses/i2c-viai2c-common.c index 3e565d5ee4c7..0fd2554731ca 100644 --- a/drivers/i2c/busses/i2c-viai2c-common.c +++ b/drivers/i2c/busses/i2c-viai2c-common.c @@ -22,12 +22,37 @@ int viai2c_check_status(struct viai2c *i2c) { int ret = 0; unsigned long time_left; + unsigned long delta_ms; time_left = wait_for_completion_timeout(&i2c->complete, msecs_to_jiffies(500)); if (!time_left) return -ETIMEDOUT; + /* + * During each byte access, the host performs clock stretching. + * In this case, the thread may be interrupted by preemption, + * resulting in a long stretching time. + * + * However, some touchpad can only tolerate host clock stretching + * of no more than 200 ms. We reduce the impact of this through + * a retransmission mechanism. + * + * Since __i2c_lock_bus_helper() is used to ensure that the + * current access will not be interrupted by the other access, + * We don't need to worry about arbitration anymore. + */ + local_irq_disable(); + i2c->t2 = ktime_get(); + delta_ms = ktime_to_ms(ktime_sub(i2c->t2, i2c->t1)); + if (delta_ms > VIAI2C_STRETCHING_TIMEOUT) { + local_irq_enable(); + dev_warn(i2c->dev, "thread blocked more than %ldms\n", delta_ms); + return -EAGAIN; + } + i2c->t1 = i2c->t2; + local_irq_enable(); + if (i2c->cmd_status & VIAI2C_ISR_NACK_ADDR) ret = -EIO; @@ -158,6 +183,7 @@ int viai2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num) int ret = 0; struct viai2c *i2c = i2c_get_adapdata(adap); + i2c->t2 = i2c->t1 = ktime_get(); for (i = 0; ret >= 0 && i < num; i++) { pmsg = &msgs[i]; if (!(pmsg->flags & I2C_M_NOSTART)) { diff --git a/drivers/i2c/busses/i2c-viai2c-common.h b/drivers/i2c/busses/i2c-viai2c-common.h index 28799e7e97f0..d0ffba22104d 100644 --- a/drivers/i2c/busses/i2c-viai2c-common.h +++ b/drivers/i2c/busses/i2c-viai2c-common.h @@ -49,6 +49,7 @@ #define VIAI2C_REG_MCR 0x0E #define VIAI2C_TIMEOUT (msecs_to_jiffies(1000)) +#define VIAI2C_STRETCHING_TIMEOUT 200 struct viai2c { struct i2c_adapter adapter; @@ -59,6 +60,8 @@ struct viai2c { u16 tcr; int irq; u16 cmd_status; + ktime_t t1; + ktime_t t2; }; int viai2c_wait_bus_not_busy(struct viai2c *i2c); -- 2.34.1
