Re: [PATCH 8/9] drm/i915/dp: Protect link training with connection mutex

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 12, 2017 at 04:57:29PM -0700, Dhinakaran Pandiyan wrote:
> The other instances of link training are protected with
> connection_mutex, so do the same in check_mst_status() too.
> 
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index aab9ba31f79e..644463ba313e 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4191,6 +4191,7 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
>  static int
>  intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  {
> +	struct drm_device *dev = intel_dp_to_dev(intel_dp);
>  	bool bret;
>  	u8 esi[DP_DPRX_ESI_LEN] = { 0 };
>  	int ret = 0;
> @@ -4205,8 +4206,11 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  		if (intel_dp->active_mst_links &&
>  		    !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
>  			DRM_DEBUG_KMS("channel EQ not ok, retraining\n");
> +
> +			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>  			intel_dp_start_link_train(intel_dp);
>  			intel_dp_stop_link_train(intel_dp);
> +			drm_modeset_unlock(&dev->mode_config.connection_mutex);

This can deadlock. We should not grab any modeset locks from the
dig_work. I had some patches at some point to move the link training to
the hotplug work so SST. I don't think I had the MST side really sorted
out at any point.

>  		}
>  
>  		DRM_DEBUG_KMS("got esi %3ph\n", esi);
> -- 
> 2.11.0

-- 
Ville Syrjälä
Intel OTC
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