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

[Harry Wentland <harry.wentland@amd.com>]

On 2/27/23 12:12, Jani Nikula wrote:
> On Mon, 27 Feb 2023, Harry Wentland <harry.wentland@amd.com> wrote:
>> On 2/26/23 09:10, Yaroslav Bolyukin 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
>>>
>>
>> According to the errata this should only apply to VII timings. The way
>> it is currently implemented will make it apply to everything which is
>> not what we want.
>>
>> Can we add this field to drm_mode_info instead of drm_display_info and
>> set it inside drm_mode_displayid_detailed when parsing a type_7 timing?
> 
> That's actually difficult to do nicely. I think the patch at hand is
> fine, and it's fine to add the information to drm_display_info. It's a
> dependency to parsing the modes.
> 
> How the info will actually be used is a different matter, and obviously
> needs to follow the spec. As it is, *this* patch doesn't say anything
> about that. But whether it's handled in VII timings parsing or
> elsewhere, I still think this part is fine.
> 

This patch itself is okay but without further work can't be used by
drivers since they don't currently have an indication whether a mode
is based on a VII timing.

Harry

> 
> BR,
> Jani.
> 
>>
>> Harry
>>
>>
>>> Signed-off-by: Yaroslav Bolyukin <iam@lach.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);
>>> +
>>>  	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
>>> +	 */
>>> +	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 */
>>
>