Re: [PATCH 5/6] drm/i915/dp: push eDP caching out into a work queue

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

On Wed, Mar 05, 2014 at 02:48:30PM -0800, Jesse Barnes wrote:
> It takes awhile to fetch the DPCD and EDID for caching, so take it out
> of the critical path to improve init time.
> 
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 113 +++++++++++++++++++++++++++++-----------
>  1 file changed, 82 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 738c4e6..763f235 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3001,6 +3001,20 @@ intel_dp_handle_test_request(struct intel_dp *intel_dp)
>  	intel_dp_aux_native_write_1(intel_dp, DP_TEST_RESPONSE, DP_TEST_NAK);
>  }
>  
> +static void intel_flush_edp_cache_work(struct intel_dp *intel_dp)
> +{
> +	struct drm_device *dev = intel_dp->attached_connector->base.dev;
> +
> +	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
> +
> +	if (!is_edp(intel_dp))
> +		return;
> +
> +	mutex_unlock(&dev->mode_config.mutex);
> +	flush_work(&intel_dp->edp_cache_work);
> +	mutex_lock(&dev->mode_config.mutex);

This feels like deadlock land to me. If we drop mode_config.mutex
someone else might grab it and then get blocked on the crtc mutex
we're already holding, and then we try to re-grab mode_config.mutex...

-- 
Ville Syrjälä
Intel OTC