[Intel-gfx] [PATCH] drm/i915/dp: add lane_count check in intel_dp_check_link_status

[Ville Syrjälä]

On Sat, Aug 27, 2016 at 02:33:25PM +0100, Matthew Auld wrote:
> Currently it's entirely possible to go through the link training step
> without first determining the lane_count, which is silly since we end up
> doing a bunch of aux transfers of size = 0, as highlighted by
> WARN_ON(!msg->buffer != !msg->size), and can only ever result in a
> 'failed to update link training' message. This can be observed during
> intel_dp_long_pulse where we can do the link training step, but before
> we have had a chance to set the link params. To avoid this we add an
> extra check for the lane_count in intel_dp_check_link_status, which
> should prevent us from doing the link training step prematurely.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=97344
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index a3c7dd8..0dbb672 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3927,6 +3927,9 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>  	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
>  		return;
>  
> +	if (!intel_dp->lane_count)
> +		return;

This pretty much amounts to the same thing that I did with 'active_streams' in 
my series [1]. The problem is that we need to sync up the state on readout to
make it really work. Daniel wasn't too happy with my .sync_state() hook, so
maybe we need something fancier.

[1] https://patchwork.freedesktop.org/series/10354/

> +
>  	/* if link training is requested we should perform it always */
>  	if ((intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) ||
>  	    (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
> -- 
> 2.7.4
> 
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-- 
Ville Syrjälä
Intel OTC