[PATCH 1/3] i915/display/intel_dp: Read PCON DSC ENC caps only for DPCD rev >= 1.4

[Ville Syrjälä]

On Thu, Feb 04, 2021 at 12:18:40PM +0530, Ankit Nautiyal wrote:
> DP-HDMI2.1 PCON has DSC encoder caps defined in registers 0x92-0x9E.
> Do not read the registers if DPCD rev < 1.4.
> 
> Fixes: https://gitlab.freedesktop.org/drm/intel/-/issues/2868
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 8c12d5375607..2b83f0f433a2 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2489,9 +2489,11 @@ static void intel_dp_get_pcon_dsc_cap(struct intel_dp *intel_dp)
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  
>  	/* Clear the cached register set to avoid using stale values */
> -
>  	memset(intel_dp->pcon_dsc_dpcd, 0, sizeof(intel_dp->pcon_dsc_dpcd));
>  
> +	if (intel_dp->dpcd[DP_DPCD_REV] < 0x14)
> +		return;
> +

Can't check the spec, but makes sense that this stuff is only valid
for recent DCPD revisions.

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

>  	if (drm_dp_dpcd_read(&intel_dp->aux, DP_PCON_DSC_ENCODER,
>  			     intel_dp->pcon_dsc_dpcd,
>  			     sizeof(intel_dp->pcon_dsc_dpcd)) < 0)
> -- 
> 2.29.2

-- 
Ville Syrjälä
Intel