[Intel-gfx] [PATCH v2 1/2] drm: Add retries for lspcon status check

[Imre Deak]

On Mon, Aug 21, 2017 at 06:55:47PM +0530, Shashank Sharma wrote:
> It's an observation during some CI tests that few LSPCON chips
> respond slow while system is under load, and need some delay
> while reading current mode status using i2c-over-aux channel.
> 
> This patch:
> - Adds few retries and delays before declaring a read
>   failure from LSPCON hardware.
> - Changes the debug level of the print from ERROR->DEBUG
>   whereas another patch in I915 will add an ERROR message
>   from the caller when we have timed out all our limits.
> 
> V2: addressed review comments from Imre, and added r-b
>     - use int instead of u8 for counter
>     - use for loop instead of do...while();
> 
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> 
> Reviewed-by: Imre Deak <imre.deak at intel.com>
> Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>
> Signed-off-by: Mahesh Kumar <mahesh1.kumar at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_dual_mode_helper.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> index 80e62f6..fc8c7ac 100644
> --- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> @@ -409,6 +409,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
>  			enum drm_lspcon_mode *mode)
>  {
>  	u8 data;
> +	int retry;
>  	int ret = 0;
>  
>  	if (!mode) {
> @@ -417,10 +418,17 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
>  	}
>  
>  	/* Read Status: i2c over aux */
> -	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_LSPCON_CURRENT_MODE,
> -				    &data, sizeof(data));
> +	for (retry = 5; ; retry--) {

Ok, confused myself with my original suggestion to include above the
condition for retry too. That could add an extraneous delay if all the
transfers fail as you explained on IRC.

I think this is still a bit clearer than the do {} while() loop so let's
go with this version.

> +		ret = drm_dp_dual_mode_read(adapter,
> +					    DP_DUAL_MODE_LSPCON_CURRENT_MODE,
> +					    &data, sizeof(data));
> +		if (!ret || !retry)
> +			break;
> +		usleep_range(500, 1000);
> +	}
> +
>  	if (ret < 0) {
> -		DRM_ERROR("LSPCON read(0x80, 0x41) failed\n");
> +		DRM_DEBUG_KMS("LSPCON read(0x80, 0x41) failed\n");
>  		return -EFAULT;
>  	}
>  
> -- 
> 2.7.4
>