[PATCH v4 1/3] drm: Add retries for lspcon mode detection

[Jani Nikula]

On Thu, 12 Oct 2017, Shashank Sharma <shashank.sharma at intel.com> wrote:
> From the CI builds, its been observed that during a driver
> reload/insert, dp dual mode read function sometimes fails to
> read from LSPCON device over i2c-over-aux channel.
>
> This patch:
> - adds some delay and few retries, allowing a scope for these
>   devices to settle down and respond.
> - changes one error log's level from ERROR->DEBUG as we want
>   to call it an error only after all the retries are exhausted.
>
> V2: Addressed review comments from Jani (for loop for retry)
> V3: Addressed review comments from Imre (break on partial read too)
> V3: Addressed review comments from Ville/Imre (Add the retries
>     exclusively for LSPCON, not for all dp_dual_mode devices)
> V4: Added r-b from Imre, sending it to dri-devel (Jani)
>
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
>
> Reviewed-by: Imre Deak <imre.deak at intel.com>
> Signed-off-by: Shashank Sharma <shashank.sharma at intel.com>

Pushed via drm-intel with Dave's IRC ack. Thanks for the patch and
review.

BR,
Jani.

> ---
>  drivers/gpu/drm/drm_dp_dual_mode_helper.c | 16 +++++++++++++---
>  1 file changed, 13 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 0ef9011..02a5092 100644
> --- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> @@ -410,6 +410,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
>  {
>  	u8 data;
>  	int ret = 0;
> +	int retry;
>  
>  	if (!mode) {
>  		DRM_ERROR("NULL input\n");
> @@ -417,10 +418,19 @@ 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 = 0; retry < 6; retry++) {
> +		if (retry)
> +			usleep_range(500, 1000);
> +
> +		ret = drm_dp_dual_mode_read(adapter,
> +					    DP_DUAL_MODE_LSPCON_CURRENT_MODE,
> +					    &data, sizeof(data));
> +		if (!ret)
> +			break;
> +	}
> +
>  	if (ret < 0) {
> -		DRM_ERROR("LSPCON read(0x80, 0x41) failed\n");
> +		DRM_DEBUG_KMS("LSPCON read(0x80, 0x41) failed\n");
>  		return -EFAULT;
>  	}

-- 
Jani Nikula, Intel Open Source Technology Center