Re: [PATCH v2 1/3] drm/dp_mst: add passthrough_aux to struct drm_dp_mst_port

[Lyude Paul <lyude@redhat.com>]

lgtm!

Reviewed-by: Lyude Paul <lyude@redhat.com>

On Fri, 2022-08-05 at 17:13 -0400, Hamza Mahfooz wrote:
> Currently, there is no way to identify if DSC pass-through can be
> enabled and what aux DSC pass-through requests ought to be sent to. So,
> add a variable to struct drm_dp_mst_port that keeps track of the
> aforementioned information.
> 
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
> ---
> v2: define DP_DSC_PASSTHROUGH_IS_SUPPORTED
> ---
>  drivers/gpu/drm/display/drm_dp_mst_topology.c | 4 +++-
>  include/drm/display/drm_dp.h                  | 1 +
>  include/drm/display/drm_dp_mst_helper.h       | 3 +++
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 67b3b9697da7..71915afd9892 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -5921,8 +5921,10 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
>  		/* Enpoint decompression with DP-to-DP peer device */
>  		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
>  		    (endpoint_fec & DP_FEC_CAPABLE) &&
> -		    (upstream_dsc & 0x2) /* DSC passthrough */)
> +		    (upstream_dsc & DP_DSC_PASSTHROUGH_IS_SUPPORTED)) {
> +			port->passthrough_aux = &immediate_upstream_port->aux;
>  			return &port->aux;
> +		}
>  
>  		/* Virtual DPCD decompression with DP-to-DP peer device */
>  		return &immediate_upstream_port->aux;
> diff --git a/include/drm/display/drm_dp.h b/include/drm/display/drm_dp.h
> index 9e3aff7e68bb..4d0abe4c7ea9 100644
> --- a/include/drm/display/drm_dp.h
> +++ b/include/drm/display/drm_dp.h
> @@ -239,6 +239,7 @@
>  
>  #define DP_DSC_SUPPORT                      0x060   /* DP 1.4 */
>  # define DP_DSC_DECOMPRESSION_IS_SUPPORTED  (1 << 0)
> +# define DP_DSC_PASSTHROUGH_IS_SUPPORTED    (1 << 1)
>  
>  #define DP_DSC_REV                          0x061
>  # define DP_DSC_MAJOR_MASK                  (0xf << 0)
> diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
> index 10adec068b7f..4a39c95f8afd 100644
> --- a/include/drm/display/drm_dp_mst_helper.h
> +++ b/include/drm/display/drm_dp_mst_helper.h
> @@ -86,6 +86,8 @@ struct drm_dp_vcpi {
>   * @next: link to next port on this branch device
>   * @aux: i2c aux transport to talk to device connected to this port, protected
>   * by &drm_dp_mst_topology_mgr.base.lock.
> + * @passthrough_aux: parent aux to which DSC pass-through requests should be
> + * sent, only set if DSC pass-through is possible.
>   * @parent: branch device parent of this port
>   * @vcpi: Virtual Channel Payload info for this port.
>   * @connector: DRM connector this port is connected to. Protected by
> @@ -140,6 +142,7 @@ struct drm_dp_mst_port {
>  	 */
>  	struct drm_dp_mst_branch *mstb;
>  	struct drm_dp_aux aux; /* i2c bus for this port? */
> +	struct drm_dp_aux *passthrough_aux;
>  	struct drm_dp_mst_branch *parent;
>  
>  	struct drm_dp_vcpi vcpi;

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat