[PATCH 10/11] drm/i915/dp_mst: Make HBLANK expansion quirk work for logical ports

[Nautiyal, Ankit K]

On 3/21/2024 1:41 AM, Imre Deak wrote:
> The DPCD OUI of the logical port on a Dell UHBR monitor - on which the
> AUX device is used to enable DSC - is all 0. To detect if the HBLANK
> expansion quirk is required for this monitor use the OUI of the port's
> parent instead.
>
> Since in the above case the DPCD of both the logical port and the parent
> port reports being a sink device (vs. branch device) type, read the
> proper sink/branch OUI based on the DPCD device type.
>
> This is required by a follow-up patch enabling the quirk for the above
> Dell monitor.
>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_dp_mst.c | 22 +++++++++++++++------
>   1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 516b00f791420..76a8fb21b8e52 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -1512,23 +1512,33 @@ intel_dp_mst_read_decompression_port_dsc_caps(struct intel_dp *intel_dp,
>   static bool detect_dsc_hblank_expansion_quirk(const struct intel_connector *connector)
>   {
>   	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> +	struct drm_dp_aux *aux = connector->dp.dsc_decompression_aux;
>   	struct drm_dp_desc desc;
>   	u8 dpcd[DP_RECEIVER_CAP_SIZE];
>   
> -	if (!connector->dp.dsc_decompression_aux)
> +	if (!aux)
>   		return false;
>   
> -	if (drm_dp_read_desc(connector->dp.dsc_decompression_aux,
> -			     &desc, true) < 0)
> +	/*
> +	 * A logical port's OUI (at least for affected sinks) is all 0, so
> +	 * instead of that the parent port's OUI is used for identification.
> +	 */
> +	if (drm_dp_mst_port_is_logical(connector->port)) {
> +		aux = drm_dp_mst_aux_for_parent(connector->port);
> +		if (!aux)
> +			aux = &connector->mst_port->aux;


As I understand, we are setting connector->mst_port as intel_dp, in the 
caller intel_dp_add_mst_connector so its unlikely that aux can be NULL, 
but do you see if we need to check for aux?

Regards,

Ankit

> +	}
> +
> +	if (drm_dp_read_dpcd_caps(aux, dpcd) < 0)
> +		return false;
> +
> +	if (drm_dp_read_desc(aux, &desc, drm_dp_is_branch(dpcd)) < 0)
>   		return false;
>   
>   	if (!drm_dp_has_quirk(&desc,
>   			      DP_DPCD_QUIRK_HBLANK_EXPANSION_REQUIRES_DSC))
>   		return false;
>   
> -	if (drm_dp_read_dpcd_caps(connector->dp.dsc_decompression_aux, dpcd) < 0)
> -		return false;
> -
>   	if (!(dpcd[DP_RECEIVE_PORT_0_CAP_0] & DP_HBLANK_EXPANSION_CAPABLE))
>   		return false;
>