Re: [PATCH] drm/i915/dp: add lane_count check in intel_dp_check_link_status

[Mika Kahola <mika.kahola@intel.com>]

On Sat, 2016-08-27 at 14:33 +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@linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld@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;
> +
>  	/* 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))) {

Should we place this check as part drm_dp_helper()'s
drm_dp_channel_eq_ok() routine as this may happen with other than our
i915 driver as well?

-- 
Mika Kahola - Intel OTC

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