On 08/21/2012 07:39 AM, Clark, Rob wrote:
On Tue, Aug 21, 2012 at 1:01 AM, Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote:
On Mon, 2012-08-20 at 20:47 -0500, Ricardo Neri wrote:
Hello!
I have been working on prototypes for the ASoC OMAP HDMI audio driver to
propagate events from the HDMI output (e.g., display getting
enabled/disabled/suspended). This for the users of the driver to react
to such events. For instance, if the display is disabled or disconected,
audio could be stopped, rerouted or whatever other decision the user
makes. This is needed because, if, for instance, the HDMI IP goes off,
audio will stall and the audio users will only see a "playback write
error (DMA or IRQ trouble?)"
In my prototypes I have used snd_soc_jack for this purpose and I have
some questions:
*I see snd_soc_jack is used mostly for headsets and microphones with
actual external mechanical connections. Strictly, in my case I propagate
events originated by the OMAP display driver (changes in the power
state), and not from external events. Some of these events are generated
from an actual HDMI cable connection/disconnection, though.
*Maybe the event should be propagated by omapdss/omapdrm/drm and the
entity in charge of the audio policy should listen those events instead.
*I do see SND_JACK_VIDEOOUT and SND_JACK_AVOUT types so maybe it is
feasible for an audio driver to report events from an AV output.
I was wondering about how much sense does it make to you guys use a
snd_soc_jack in this case?
How does DRM handle audio? I made a quick grep, but I see the drm
drivers only enabling the audio in the HW, nothing else.
I confess to not knowing too much about audio/alsa, but what does
audio driver need from hdmi? Just hotplug events?
At least for the case of the ASoC HDMI audio driver (but hopefully for
other audio drivers as well), it needs to detect whether an HDMI output
is available, if the display's current configuration supports audio
(e.g., a 1080p display configured as VGA should be reported as not
supporting audio). It also needs interfaces to
configure/prepare/start/stop audio. Also, of course, needs to know if
the display is off/on/suspended and when transitions occur. For OMAP,
omapdss provide an interface for this functionality for ALSA or any
other interested user.
From a quick look, it seems most of what the existing drm drivers are
doing is detecting if the display supports audio, and then turning
on/off the hw.. (and some infoframe stuff in some cases).
Yes, it seems to me that every driver makes its own audio
implementation, mainly focused on configuration. I could not find any
audio common interface so that users like ALSA can take advantage of.
Also, I could not see any ALSA driver using functionality provided by a
drm driver.
Maybe the lack of audio support in drm is because the audio users should
not talk to drm directly but to a lower level component (omapdrm,
omapdss?). However, today there exists video technology supports audio
as well, such as DisplayPort or HDMI. Could it make more sense now to
provide audio support?
Does ASoC support 'hotplug' of audio devices? If so, maybe it makes
some sense to have some support in drm core. At least all the edid
parsing stuff to determine if the display supports audio should be
generic and not driver specific.
drm already supports generic edid parsing to check for audio support.
This is a good example of how an audio driver could just use that
functionality to probe audio support.
Ricardo
BR,
-R
If there's a common generic way to handle this, we should obviously use
that. But if we need to choose between doing something custom or doing
it in omapdrm driver, I think we should go for drm the only solution and
forget about audio with omapfb.
Tomi
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