linux-kernel - Re: [PATCH v3 1/2] drm/edid: parse DRM VESA dsc bpp target

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Message-ID: <874jr72x4s.fsf@intel.com>
Date:   Mon, 27 Feb 2023 12:58:11 +0200
From:   Jani Nikula <jani.nikula@...el.com>
To:     Yaroslav Bolyukin <iam@...h.pw>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     Harry Wentland <harry.wentland@....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@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Yaroslav Bolyukin <iam@...h.pw>
Subject: Re: [PATCH v3 1/2] drm/edid: parse DRM VESA dsc bpp target

On Sun, 26 Feb 2023, Yaroslav Bolyukin <iam@...h.pw> wrote:
> As per DisplayID v2.0 Errata E9 spec "DSC pass-through timing support"
> VESA vendor-specific data block may contain target DSC bits per pixel
> fields
>
> Signed-off-by: Yaroslav Bolyukin <iam@...h.pw>
> ---
>  drivers/gpu/drm/drm_edid.c  | 38 +++++++++++++++++++++++++------------
>  include/drm/drm_connector.h |  6 ++++++
>  include/drm/drm_displayid.h |  4 ++++
>  3 files changed, 36 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 3d0a4da661bc..aa88ac82cbe0 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -6338,7 +6338,7 @@ static void drm_parse_vesa_mso_data(struct drm_connector *connector,
>  	if (oui(vesa->oui[0], vesa->oui[1], vesa->oui[2]) != VESA_IEEE_OUI)
>  		return;
>  
> -	if (sizeof(*vesa) != sizeof(*block) + block->num_bytes) {
> +	if (block->num_bytes < 5) {
>  		drm_dbg_kms(connector->dev,
>  			    "[CONNECTOR:%d:%s] Unexpected VESA vendor block size\n",
>  			    connector->base.id, connector->name);
> @@ -6361,24 +6361,37 @@ static void drm_parse_vesa_mso_data(struct drm_connector *connector,
>  		break;
>  	}
>  
> -	if (!info->mso_stream_count) {
> -		info->mso_pixel_overlap = 0;
> -		return;
> -	}
> +	info->mso_pixel_overlap = 0;
> +
> +	if (info->mso_stream_count) {
> +		info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
> +
> +		if (info->mso_pixel_overlap > 8) {
> +			drm_dbg_kms(connector->dev,
> +				    "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value %u\n",
> +				    connector->base.id, connector->name,
> +				    info->mso_pixel_overlap);
> +			info->mso_pixel_overlap = 8;
> +		}
>  
> -	info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
> -	if (info->mso_pixel_overlap > 8) {
>  		drm_dbg_kms(connector->dev,
> -			    "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value %u\n",
> +			    "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
>  			    connector->base.id, connector->name,
> -			    info->mso_pixel_overlap);
> -		info->mso_pixel_overlap = 8;
> +			    info->mso_stream_count, info->mso_pixel_overlap);
> +	}
> +
> +	if (block->num_bytes < 7) {
> +		/* DSC bpp is optional */
> +		return;
>  	}
>  
> +	info->dp_dsc_bpp = FIELD_GET(DISPLAYID_VESA_DSC_BPP_INT, vesa->dsc_bpp_int) * 16
> +		+ FIELD_GET(DISPLAYID_VESA_DSC_BPP_FRACT, vesa->dsc_bpp_fract);
> +

Matter of taste, but I'd probably use << 4 and |. *shrug*

>  	drm_dbg_kms(connector->dev,
> -		    "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
> +		    "[CONNECTOR:%d:%s] DSC bits per pixel %u\n",
>  		    connector->base.id, connector->name,
> -		    info->mso_stream_count, info->mso_pixel_overlap);
> +		    info->dp_dsc_bpp);
>  }
>  
>  static void drm_update_mso(struct drm_connector *connector,
> @@ -6425,6 +6438,7 @@ static void drm_reset_display_info(struct drm_connector *connector)
>  	info->mso_stream_count = 0;
>  	info->mso_pixel_overlap = 0;
>  	info->max_dsc_bpp = 0;
> +	info->dp_dsc_bpp = 0;
>  
>  	kfree(info->vics);
>  	info->vics = NULL;
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 7b5048516185..1d01e0146a7f 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -719,6 +719,12 @@ struct drm_display_info {
>  	 */
>  	u32 max_dsc_bpp;
>  
> +	/**
> +	 * @dp_dsc_bpp: DP Display-Stream-Compression (DSC) timing's target
> +	 * DST bits per pixel in 6.4 fixed point format. 0 means undefined

DST?

Reviewed-by: Jani Nikula <jani.nikula@...el.com>

> +	 */
> +	u16 dp_dsc_bpp;
> +
>  	/**
>  	 * @vics: Array of vics_len VICs. Internal to EDID parsing.
>  	 */
> diff --git a/include/drm/drm_displayid.h b/include/drm/drm_displayid.h
> index 49649eb8447e..0fc3afbd1675 100644
> --- a/include/drm/drm_displayid.h
> +++ b/include/drm/drm_displayid.h
> @@ -131,12 +131,16 @@ struct displayid_detailed_timing_block {
>  
>  #define DISPLAYID_VESA_MSO_OVERLAP	GENMASK(3, 0)
>  #define DISPLAYID_VESA_MSO_MODE		GENMASK(6, 5)
> +#define DISPLAYID_VESA_DSC_BPP_INT	GENMASK(5, 0)
> +#define DISPLAYID_VESA_DSC_BPP_FRACT	GENMASK(3, 0)
>  
>  struct displayid_vesa_vendor_specific_block {
>  	struct displayid_block base;
>  	u8 oui[3];
>  	u8 data_structure_type;
>  	u8 mso;
> +	u8 dsc_bpp_int;
> +	u8 dsc_bpp_fract;
>  } __packed;
>  
>  /* DisplayID iteration */

-- 
Jani Nikula, Intel Open Source Graphics Center