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

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

On Fri, 11 Mar 2016, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> [ text/plain ]
> On Fri, Mar 11, 2016 at 03:36:48PM +0200, Jani Nikula wrote:
>> 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... ;)
>
> Since sad_count will not exceed 15-total_sad_count, total_sad_count will never
> exceed 15.

Right. I guess it could be spelled out for folks like me. :/

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

If you run out of things to do (that'll be the day), you could follow up
with replacing some of the magic here for offsets etc. with the
DRM_ELD_* defines I added in drm_edid.h.

BR,
Jani.


>
>> 
>> 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

-- 
Jani Nikula, Intel Open Source Technology Center
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