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

[Ville Syrjälä]

On Wed, Oct 19, 2016 at 10:29:53PM +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.
> 
> v2: add WARN_ON_ONCE and FIXME comment (Ville)
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=97344
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Mika Kahola <mika.kahola at intel.com>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 88f3b74..fb760ad 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4032,6 +4032,11 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>  	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
>  		return;
>  
> +	/* FIXME: we need to synchronize this sort of stuff with hardware
> +	 * readout */
> +	if (WARN_ON_ONCE(!intel_dp->lane_count))
> +		return;

One warn is better than a constant spew as can be seen eg. in
https://bugs.freedesktop.org/show_bug.cgi?id=98323

Still need to fix the real issue of course, but in the meantime

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> +
>  	/* 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

-- 
Ville Syrjälä
Intel OTC