linux-kernel - Re: [PATCH v2 1/3] drm/dp_mst: add passthrough_aux to struct drm_dp_mst

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Message-ID: <8db8a726d1aac25b3590497db9cbdcc3fe161227.camel@redhat.com>
Date:   Fri, 05 Aug 2022 17:17:46 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Hamza Mahfooz <hamza.mahfooz@....com>, linux-kernel@...r.kernel.org
Cc:     Harry Wentland <harry.wentland@....com>,
        Fangzhi Zuo <Jerry.Zuo@....com>, Wayne Lin <Wayne.Lin@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        hersenxs.wu@....com, Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mikita Lipski <mikita.lipski@....com>,
        Claudio Suarez <cssk@...-c.es>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Roman Li <Roman.Li@....com>, Ian Chen <ian.chen@....com>,
        Colin Ian King <colin.king@...el.com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jani Nikula <jani.nikula@...el.com>,
        Imran Khan <imran.f.khan@...cle.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Imre Deak <imre.deak@...el.com>,
        David Zhang <dingchen.zhang@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 1/3] drm/dp_mst: add passthrough_aux to struct
 drm_dp_mst_port

lgtm!

Reviewed-by: Lyude Paul <lyude@...hat.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@....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