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

From: Jani Nikula
Date: Mon Feb 27 2023 - 14:18:21 EST

On Mon, 27 Feb 2023, Harry Wentland <harry.wentland@xxxxxxx> wrote:
> On 2/27/23 12:12, Jani Nikula wrote:
>> On Mon, 27 Feb 2023, Harry Wentland <harry.wentland@xxxxxxx> 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.

Right, agreed.

All I'm saying is info->dp_dsc_bpp is the way to pass that info from
VESA vendor block to mode parsing.

Come to think of it, this patch should probably also rename
drm_update_mso() and drm_parse_vesa_mso_data() to reflect the more
generic VESA vendor block parsing instead of just MSO.

BR,
Jani.

>
> Harry
>
>>
>> BR,
>> Jani.
>>
>>>
>>> Harry
>>>
>>>
>>>> Signed-off-by: Yaroslav Bolyukin <iam@xxxxxxx>
>>>> ---
>>>> 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 */
>>>
>>
>

--
Jani Nikula, Intel Open Source Graphics Center