On Thu, 12 Oct 2017, Shashank Sharma <shashank.sha...@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.syrj...@linux.intel.com>
> Cc: Imre Deak <imre.d...@intel.com>
> Cc: Jani Nikula <jani.nik...@linux.intel.com>
>
> Reviewed-by: Imre Deak <imre.d...@intel.com>
> Signed-off-by: Shashank Sharma <shashank.sha...@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
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