Re: [PATCH v3] i2c: nvidia-gpu: Handle timeout correctly in gpu_i2c_check_status()

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Mar 24, 2020 at 11:28:11PM +0800, Kai-Heng Feng wrote:
> Nvidia card may come with a "phantom" UCSI device, and its driver gets
> stuck in probe routine, prevents any system PM operations like suspend.
> 
> There's an unaccounted case that the target time can equal to jiffies in
> gpu_i2c_check_status(), let's solve that by using readl_poll_timeout()
> instead of jiffies comparison functions. 
> 

Thank you!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>


> Fixes: c71bcdcb42a7 ("i2c: add i2c bus driver for NVIDIA GPU")
> Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
> v3:
> - Use readl_poll_timeout to make the retry loop simpler.
> 
> v2:
> - Use a boolean to make sure the operation is timeout or not.
> 
>  drivers/i2c/busses/i2c-nvidia-gpu.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-nvidia-gpu.c b/drivers/i2c/busses/i2c-nvidia-gpu.c
> index 62e18b4db0ed..f5d25ce00f03 100644
> --- a/drivers/i2c/busses/i2c-nvidia-gpu.c
> +++ b/drivers/i2c/busses/i2c-nvidia-gpu.c
> @@ -8,6 +8,7 @@
>  #include <linux/delay.h>
>  #include <linux/i2c.h>
>  #include <linux/interrupt.h>
> +#include <linux/iopoll.h>
>  #include <linux/module.h>
>  #include <linux/pci.h>
>  #include <linux/platform_device.h>
> @@ -75,20 +76,15 @@ static void gpu_enable_i2c_bus(struct gpu_i2c_dev *i2cd)
>  
>  static int gpu_i2c_check_status(struct gpu_i2c_dev *i2cd)
>  {
> -	unsigned long target = jiffies + msecs_to_jiffies(1000);
>  	u32 val;
> +	int ret;
>  
> -	do {
> -		val = readl(i2cd->regs + I2C_MST_CNTL);
> -		if (!(val & I2C_MST_CNTL_CYCLE_TRIGGER))
> -			break;
> -		if ((val & I2C_MST_CNTL_STATUS) !=
> -				I2C_MST_CNTL_STATUS_BUS_BUSY)
> -			break;
> -		usleep_range(500, 600);
> -	} while (time_is_after_jiffies(target));
> -
> -	if (time_is_before_jiffies(target)) {
> +	ret = readl_poll_timeout(i2cd->regs + I2C_MST_CNTL, val,
> +				 !(val & I2C_MST_CNTL_CYCLE_TRIGGER) ||
> +				 (val & I2C_MST_CNTL_STATUS) != I2C_MST_CNTL_STATUS_BUS_BUSY,
> +				 500, 1000 * USEC_PER_MSEC);
> +
> +	if (ret) {
>  		dev_err(i2cd->dev, "i2c timeout error %x\n", val);
>  		return -ETIMEDOUT;
>  	}
> -- 
> 2.17.1
> 

-- 
With Best Regards,
Andy Shevchenko