Re: [PATCH] drm/edid: Extract SADs properly from multiple audio data blocks

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

On Wed, 09 Mar 2016, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> SADs may span multiple CEA audio data blocks in the EDID.
>
> CEA-861-E says:
> "The order of the Data Blocks is not constrained. It is also possible
> to have more than one of a specific type of data block if necessary to
> include all of the descriptors needed to describe the sink’s capabilities."
>
> Each audio data block can carry up to 10 SADs, whereas the ELD SAD limit
> is 15 according to HDA 1.0a spec. So we should support at least two data
> blocks. And apparently some devices take a more liberal interpretation
> and stuff only one SAD per data block even when they would fit into one.
>
> So let's try to extract all the SADs we can fit into the ELD even when
> they span multiple data blocks.
>
> While at it, toss in a comment to explain the 13 byte monitor name
> string limit which confused me at first.
>
> Cc: Arturo Pérez <artur999555@gmail.com>
> Tested-by: Arturo Pérez <artur999555@gmail.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94197
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index fdb1eb014586..414d7f61aa05 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3308,7 +3308,7 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
>  	u8 *cea;
>  	u8 *name;
>  	u8 *db;
> -	int sad_count = 0;
> +	int total_sad_count = 0;
>  	int mnl;
>  	int dbl;
>  
> @@ -3322,6 +3322,7 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
>  
>  	name = NULL;
>  	drm_for_each_detailed_block((u8 *)edid, monitor_name, &name);
> +	/* max: 13 bytes EDID, 16 bytes ELD */
>  	for (mnl = 0; name && mnl < 13; mnl++) {
>  		if (name[mnl] == 0x0a)
>  			break;
> @@ -3350,11 +3351,15 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
>  			dbl = cea_db_payload_len(db);
>  
>  			switch (cea_db_tag(db)) {
> +				int sad_count;
> +
>  			case AUDIO_BLOCK:
>  				/* Audio Data Block, contains SADs */
> -				sad_count = dbl / 3;
> -				if (dbl >= 1)
> -					memcpy(eld + 20 + mnl, &db[1], dbl);
> +				sad_count = min(dbl / 3, 15 - total_sad_count);

What if total_sad_count > 15? At a glance, this seems to self correct by
subtracting the excess every second time... ;)

BR,
Jani.

> +				if (sad_count >= 1)
> +					memcpy(eld + 20 + mnl + total_sad_count * 3,
> +					       &db[1], sad_count * 3);
> +				total_sad_count += sad_count;
>  				break;
>  			case SPEAKER_BLOCK:
>  				/* Speaker Allocation Data Block */
> @@ -3371,13 +3376,13 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
>  			}
>  		}
>  	}
> -	eld[5] |= sad_count << 4;
> +	eld[5] |= total_sad_count << 4;
>  
>  	eld[DRM_ELD_BASELINE_ELD_LEN] =
>  		DIV_ROUND_UP(drm_eld_calc_baseline_block_size(eld), 4);
>  
>  	DRM_DEBUG_KMS("ELD size %d, SAD count %d\n",
> -		      drm_eld_size(eld), sad_count);
> +		      drm_eld_size(eld), total_sad_count);
>  }
>  EXPORT_SYMBOL(drm_edid_to_eld);

-- 
Jani Nikula, Intel Open Source Technology Center
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