Re: [Intel-gfx] [PATCH v1 11/13] drm/edid: add HF-EEODB support to EDID read and allocation

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

On Fri, 03 Jun 2022, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Tue, May 24, 2022 at 01:39:33PM +0300, Jani Nikula wrote:
>> HDMI 2.1 section 10.3.6 defines an HDMI Forum EDID Extension Override
>> Data Block, which may contain a different extension count than the base
>> block claims. Add support for reading more EDID data if available. The
>> extra blocks aren't parsed yet, though.
>> 
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/drm_edid.c | 81 ++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 78 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>> index 5e0a91da565e..ba0c880dc133 100644
>> --- a/drivers/gpu/drm/drm_edid.c
>> +++ b/drivers/gpu/drm/drm_edid.c
>> @@ -1581,6 +1581,15 @@ static bool version_greater(const struct drm_edid *drm_edid,
>>  		(edid->version == version && edid->revision > revision);
>>  }
>>  
>> +static int edid_hfeeodb_extension_block_count(const struct edid *edid);
>> +
>> +static int edid_hfeeodb_block_count(const struct edid *edid)
>> +{
>> +	int eeodb = edid_hfeeodb_extension_block_count(edid);
>> +
>> +	return eeodb ? eeodb + 1 : 0;
>> +}
>> +
>>  static int edid_extension_block_count(const struct edid *edid)
>>  {
>>  	return edid->extensions;
>> @@ -2026,6 +2035,11 @@ static struct edid *edid_filter_invalid_blocks(struct edid *edid,
>>  	struct edid *new;
>>  	int i, valid_blocks = 0;
>>  
>> +	/*
>> +	 * Note: If the EDID uses HF-EEODB, but has invalid blocks, we'll revert
>> +	 * back to regular extension count here. We don't want to start
>> +	 * modifying the HF-EEODB extension too.
>> +	 */
>>  	for (i = 0; i < edid_block_count(edid); i++) {
>>  		const void *src_block = edid_block_data(edid, i);
>>  
>> @@ -2235,7 +2249,7 @@ static struct edid *_drm_do_get_edid(struct drm_connector *connector,
>>  				     size_t *size)
>>  {
>>  	enum edid_block_status status;
>> -	int i, invalid_blocks = 0;
>> +	int i, num_blocks, invalid_blocks = 0;
>>  	struct edid *edid, *new;
>>  	size_t alloc_size = EDID_LENGTH;
>>  
>> @@ -2277,7 +2291,8 @@ static struct edid *_drm_do_get_edid(struct drm_connector *connector,
>>  		goto fail;
>>  	edid = new;
>>  
>> -	for (i = 1; i < edid_block_count(edid); i++) {
>> +	num_blocks = edid_block_count(edid);
>> +	for (i = 1; i < num_blocks; i++) {
>>  		void *block = (void *)edid_block_data(edid, i);
>>  
>>  		status = edid_block_read(block, i, read_block, context);
>> @@ -2288,11 +2303,31 @@ static struct edid *_drm_do_get_edid(struct drm_connector *connector,
>>  			if (status == EDID_BLOCK_READ_FAIL)
>>  				goto fail;
>>  			invalid_blocks++;
>> +		} else if (i == 1) {
>> +			/*
>> +			 * If the first EDID extension is a CTA extension, and
>> +			 * the first Data Block is HF-EEODB, override the
>> +			 * extension block count.
>> +			 *
>> +			 * Note: HF-EEODB could specify a smaller extension
>> +			 * count too, but we can't risk allocating a smaller
>> +			 * amount.
>> +			 */
>> +			int eeodb = edid_hfeeodb_block_count(edid);
>> +
>> +			if (eeodb > num_blocks) {
>> +				num_blocks = eeodb;
>> +				alloc_size = edid_size_by_blocks(num_blocks);
>> +				new = krealloc(edid, alloc_size, GFP_KERNEL);
>> +				if (!new)
>> +					goto fail;
>> +				edid = new;
>> +			}
>>  		}
>>  	}
>>  
>>  	if (invalid_blocks) {
>> -		connector_bad_edid(connector, edid, edid_block_count(edid));
>> +		connector_bad_edid(connector, edid, num_blocks);
>>  
>>  		edid = edid_filter_invalid_blocks(edid, &alloc_size);
>>  	}
>> @@ -3825,6 +3860,7 @@ static int add_detailed_modes(struct drm_connector *connector,
>>  #define CTA_EXT_DB_HDR_STATIC_METADATA	6
>>  #define CTA_EXT_DB_420_VIDEO_DATA	14
>>  #define CTA_EXT_DB_420_VIDEO_CAP_MAP	15
>> +#define CTA_EXT_DB_HF_EEODB		0x78
>>  #define CTA_EXT_DB_HF_SCDB		0x79
>>  
>>  #define EDID_BASIC_AUDIO	(1 << 6)
>> @@ -4868,6 +4904,12 @@ static bool cea_db_is_hdmi_forum_vsdb(const struct cea_db *db)
>>  		cea_db_payload_len(db) >= 7;
>>  }
>>  
>> +static bool cea_db_is_hdmi_forum_eeodb(const void *db)
>> +{
>> +	return cea_db_is_extended_tag(db, CTA_EXT_DB_HF_EEODB) &&
>> +		cea_db_payload_len(db) >= 2;
>> +}
>> +
>>  static bool cea_db_is_microsoft_vsdb(const struct cea_db *db)
>>  {
>>  	return cea_db_is_vendor(db, MICROSOFT_IEEE_OUI) &&
>> @@ -4902,6 +4944,39 @@ static bool cea_db_is_hdmi_hdr_metadata_block(const struct cea_db *db)
>>  		cea_db_payload_len(db) >= 3;
>>  }
>>  
>> +/*
>> + * Get the HF-EEODB override extension block count from EDID.
>> + *
>> + * The passed in EDID may be partially read, as long as it has at least two
>> + * blocks (base block and one extension block) if EDID extension count is > 0.
>> + *
>> + * References:
>> + * - HDMI 2.1 section 10.3.6 HDMI Forum EDID Extension Override Data Block
>> + */
>> +static int edid_hfeeodb_extension_block_count(const struct edid *edid)
>> +{
>> +	const u8 *cta;
>> +
>> +	/* No extensions according to base block, no HF-EEODB. */
>> +	if (!edid_extension_block_count(edid))
>> +		return 0;
>> +
>> +	/* HF-EEODB is always in the first EDID extension block only */
>> +	cta = edid_extension_block_data(edid, 0);
>> +	if (edid_block_tag(cta) != CEA_EXT || cea_revision(cta) < 3)
>> +		return 0;
>> +
>> +	/*
>> +	 * Sinks that include the HF-EEODB in their E-EDID shall include one and
>> +	 * only one instance of the HF-EEODB in the E-EDID, occupying bytes 4
>> +	 * through 6 of Block 1 of the E-EDID.
>> +	 */
>> +	if (!cea_db_is_hdmi_forum_eeodb(&cta[4]))
>> +		return 0;
>
> Still not a big fan of these hardcoded things. Not sure if there's any
> easy way to just use the normal iterators at this point when we don't
> really know the full composition of the EDID yet. If not then I guess
> we'll have to use some hardcoded stuff. What we definitely seem to be
> missing here are size checks, for both the whoe data block collection,
> and the specific data block payload.

I don't like it either, but it's a chicken and egg problem wrt how far
to iterate. Taking this into account in the iterators looks like making
the iterators harder to understand, so I prefer the hardcoded hack here
in one place. And the spec specifically says where this data block must
be.

The data block collection size check is an oversight, but
cea_db_is_hdmi_forum_eeodb() does check for minimum payload length.

BR,
Jani.

>
>> +
>> +	return cta[4 + 2];
>> +}
>> +
>>  static void drm_parse_y420cmdb_bitmap(struct drm_connector *connector,
>>  				      const u8 *db)
>>  {
>> -- 
>> 2.30.2

-- 
Jani Nikula, Intel Open Source Graphics Center