Re: [PATCH 3/4] drm/edid: Refactor HFVSDB parsing for DSC1.2

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 11 Aug 2022, Ankit Nautiyal <ankit.k.nautiyal@intel.com> wrote:
> DSC capabilities are given in bytes 11-13 of VSDB (i.e. bytes 8-10 of
> SCDS). Since minimum length of Data block is 7, all bytes greater than 7
> must be read only after checking the length of the data block.
>
> This patch adds check for data block length before reading relavant DSC
> bytes.
>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>

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

> ---
>  drivers/gpu/drm/drm_edid.c | 93 ++++++++++++++++++++------------------
>  1 file changed, 49 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index ffff1d08b3a4..c9c3a9c8fa26 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5706,9 +5706,6 @@ static void drm_parse_ycbcr420_deep_color_info(struct drm_connector *connector,
>  static void drm_parse_dsc_info(struct drm_hdmi_dsc_cap *hdmi_dsc,
>  			       const u8 *hf_scds)
>  {
> -	u8 dsc_max_slices;
> -	u8 dsc_max_frl_rate;
> -
>  	hdmi_dsc->v_1p2 = hf_scds[11] & DRM_EDID_DSC_1P2;
>  
>  	if (!hdmi_dsc->v_1p2)
> @@ -5727,47 +5724,54 @@ static void drm_parse_dsc_info(struct drm_hdmi_dsc_cap *hdmi_dsc,
>  		/* Supports min 8 BPC if DSC1.2 is supported*/
>  		hdmi_dsc->bpc_supported = 8;
>  
> -	dsc_max_frl_rate = (hf_scds[12] & DRM_EDID_DSC_MAX_FRL_RATE_MASK) >> 4;
> -	drm_get_max_frl_rate(dsc_max_frl_rate, &hdmi_dsc->max_lanes,
> -			     &hdmi_dsc->max_frl_rate_per_lane);
> -	hdmi_dsc->total_chunk_kbytes = hf_scds[13] & DRM_EDID_DSC_TOTAL_CHUNK_KBYTES;
> +	if (cea_db_payload_len(hf_scds) >= 12 && hf_scds[12]) {
> +		u8 dsc_max_slices;
> +		u8 dsc_max_frl_rate;
>  
> -	dsc_max_slices = hf_scds[12] & DRM_EDID_DSC_MAX_SLICES;
> +		dsc_max_frl_rate = (hf_scds[12] & DRM_EDID_DSC_MAX_FRL_RATE_MASK) >> 4;
> +		drm_get_max_frl_rate(dsc_max_frl_rate, &hdmi_dsc->max_lanes,
> +				     &hdmi_dsc->max_frl_rate_per_lane);
>  
> -	switch (dsc_max_slices) {
> -	case 1:
> -		hdmi_dsc->max_slices = 1;
> -		hdmi_dsc->clk_per_slice = 340;
> -		break;
> -	case 2:
> -		hdmi_dsc->max_slices = 2;
> -		hdmi_dsc->clk_per_slice = 340;
> -		break;
> -	case 3:
> -		hdmi_dsc->max_slices = 4;
> -		hdmi_dsc->clk_per_slice = 340;
> -		break;
> -	case 4:
> -		hdmi_dsc->max_slices = 8;
> -		hdmi_dsc->clk_per_slice = 340;
> -		break;
> -	case 5:
> -		hdmi_dsc->max_slices = 8;
> -		hdmi_dsc->clk_per_slice = 400;
> -		break;
> -	case 6:
> -		hdmi_dsc->max_slices = 12;
> -		hdmi_dsc->clk_per_slice = 400;
> -		break;
> -	case 7:
> -		hdmi_dsc->max_slices = 16;
> -		hdmi_dsc->clk_per_slice = 400;
> -		break;
> -	case 0:
> -	default:
> -		hdmi_dsc->max_slices = 0;
> -		hdmi_dsc->clk_per_slice = 0;
> +		dsc_max_slices = hf_scds[12] & DRM_EDID_DSC_MAX_SLICES;
> +
> +		switch (dsc_max_slices) {
> +		case 1:
> +			hdmi_dsc->max_slices = 1;
> +			hdmi_dsc->clk_per_slice = 340;
> +			break;
> +		case 2:
> +			hdmi_dsc->max_slices = 2;
> +			hdmi_dsc->clk_per_slice = 340;
> +			break;
> +		case 3:
> +			hdmi_dsc->max_slices = 4;
> +			hdmi_dsc->clk_per_slice = 340;
> +			break;
> +		case 4:
> +			hdmi_dsc->max_slices = 8;
> +			hdmi_dsc->clk_per_slice = 340;
> +			break;
> +		case 5:
> +			hdmi_dsc->max_slices = 8;
> +			hdmi_dsc->clk_per_slice = 400;
> +			break;
> +		case 6:
> +			hdmi_dsc->max_slices = 12;
> +			hdmi_dsc->clk_per_slice = 400;
> +			break;
> +		case 7:
> +			hdmi_dsc->max_slices = 16;
> +			hdmi_dsc->clk_per_slice = 400;
> +			break;
> +		case 0:
> +		default:
> +			hdmi_dsc->max_slices = 0;
> +			hdmi_dsc->clk_per_slice = 0;
> +		}
>  	}
> +
> +	if (cea_db_payload_len(hf_scds) >= 13 && hf_scds[13])
> +		hdmi_dsc->total_chunk_kbytes = hf_scds[13] & DRM_EDID_DSC_TOTAL_CHUNK_KBYTES;
>  }
>  
>  /* Sink Capability Data Structure */
> @@ -5776,6 +5780,7 @@ static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
>  {
>  	struct drm_display_info *display = &connector->display_info;
>  	struct drm_hdmi_info *hdmi = &display->hdmi;
> +	struct drm_hdmi_dsc_cap *hdmi_dsc = &hdmi->dsc_cap;
>  
>  	display->has_hdmi_infoframe = true;
>  
> @@ -5816,17 +5821,17 @@ static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
>  
>  	if (hf_scds[7]) {
>  		u8 max_frl_rate;
> -		struct drm_hdmi_dsc_cap *hdmi_dsc = &hdmi->dsc_cap;
>  
>  		DRM_DEBUG_KMS("hdmi_21 sink detected. parsing edid\n");
>  		max_frl_rate = (hf_scds[7] & DRM_EDID_MAX_FRL_RATE_MASK) >> 4;
>  		drm_get_max_frl_rate(max_frl_rate, &hdmi->max_lanes,
>  				     &hdmi->max_frl_rate_per_lane);
> -
> -		drm_parse_dsc_info(hdmi_dsc, hf_scds);
>  	}
>  
>  	drm_parse_ycbcr420_deep_color_info(connector, hf_scds);
> +
> +	if (cea_db_payload_len(hf_scds) >= 11 && hf_scds[11])
> +		drm_parse_dsc_info(hdmi_dsc, hf_scds);
>  }
>  
>  static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,

-- 
Jani Nikula, Intel Open Source Graphics Center