Re: [alsa-devel] [RFC] ASoC: snd_soc_jack for HDMI audio: does it make sense?
On 08/21/2012 07:39 AM, Clark, Rob wrote:
On Tue, Aug 21, 2012 at 1:01 AM, Tomi Valkeinen tomi.valkeinen@ti.com 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
At Tue, 21 Aug 2012 19:58:02 -0500, Ricardo Neri wrote:
On 08/21/2012 07:39 AM, Clark, Rob wrote:
On Tue, Aug 21, 2012 at 1:01 AM, Tomi Valkeinen tomi.valkeinen@ti.com 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?
The reason is that the audio and video handling are already separated in the hardware level, at least, for desktop graphics.
The audio infoframe is passed via ELD to the audio controller part upon plug/unplugging via HD-audio unsolicited event, and the audio driver sets up the stuff according to the given ELD. Thus no extra interface between drm and ALSA was required in the kernel API level, so far.
Takashi
Hi Takashi,
On 08/22/2012 02:55 AM, Takashi Iwai wrote:
At Tue, 21 Aug 2012 19:58:02 -0500, Ricardo Neri wrote:
On 08/21/2012 07:39 AM, Clark, Rob wrote:
On Tue, Aug 21, 2012 at 1:01 AM, Tomi Valkeinen tomi.valkeinen@ti.com 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 ie · · Il y a 12 minutes ·
s
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?
The reason is that the audio and video handling are already separated in the hardware level, at least, for desktop graphics.
Separated in what sense? Do they have separate register banks in independent power domains? Can audio an video work with complete independence. What happens if someone decides to power off video. Is the audio able to continue if required?
The audio infoframe is passed via ELD to the audio controller part upon plug/unplugging via HD-audio unsolicited event, and the audio driver sets up the stuff according to the given ELD. Thus no extra interface between drm and ALSA was required in the kernel API level, so far.
I see that the unsolicited event is used only to parse the EDID, correct? It also notifies about the jack status. Hence, if there the cable is disconnected the application will know and act accordingly. Is this understanding correct?
Also, I see that hda_pcm_ops does not have a trigger or start/stop functions, how does it know when to start/stop audio. Maybe with azx_pcm_trigger?
Sorry, I am not expert in HD-audio :)
Ricardo
Takashi
On 08/23/2012 07:44 PM, Ricardo Neri wrote:
On 08/22/2012 02:55 AM, Takashi Iwai wrote:
At Tue, 21 Aug 2012 19:58:02 -0500, Ricardo Neri wrote:
...
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?
The reason is that the audio and video handling are already separated in the hardware level, at least, for desktop graphics.
Separated in what sense? Do they have separate register banks in
For NVIDIA desktop GPUs, this is certainly true, and I think so for any Intel Azalia/HDA controller. The separate register banks are in different PCI functions on the chip. The Intel Azalia/HDA spec also architects specific ways that the audio and video parts interact (i.e. ELD representation of EDID data, unsolicited response messages when the video state changes, etc.) Oh, I see Takashi mentioned this below.
independent power domains?
Most likely yes.
Can audio an video work with complete independence. What happens if someone decides to power off video. Is the audio able to continue if required?
I believe audio DMA isn't affect by the video state, but I'm not 100% sure of that.
The audio infoframe is passed via ELD to the audio controller part upon plug/unplugging via HD-audio unsolicited event, and the audio driver sets up the stuff according to the given ELD. Thus no extra interface between drm and ALSA was required in the kernel API level, so far.
I see that the unsolicited event is used only to parse the EDID, correct? It also notifies about the jack status. Hence, if there the cable is disconnected the application will know and act accordingly. Is this understanding correct?
The kernel will know, and then passes the information on to user-space.
At Thu, 23 Aug 2012 20:44:32 -0500, Ricardo Neri wrote:
Hi Takashi,
On 08/22/2012 02:55 AM, Takashi Iwai wrote:
At Tue, 21 Aug 2012 19:58:02 -0500, Ricardo Neri wrote:
On 08/21/2012 07:39 AM, Clark, Rob wrote:
On Tue, Aug 21, 2012 at 1:01 AM, Tomi Valkeinen tomi.valkeinen@ti.com 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 ie · · Il y a 12 minutes ·
s
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?
The reason is that the audio and video handling are already separated in the hardware level, at least, for desktop graphics.
Separated in what sense? Do they have separate register banks in independent power domains? Can audio an video work with complete independence. What happens if someone decides to power off video. Is the audio able to continue if required?
As Stephen already pointed, the functionality is independent in the PCI hardware level. The audio part even accepts and DMA is working without connection to the actual output.
The audio infoframe is passed via ELD to the audio controller part upon plug/unplugging via HD-audio unsolicited event, and the audio driver sets up the stuff according to the given ELD. Thus no extra interface between drm and ALSA was required in the kernel API level, so far.
I see that the unsolicited event is used only to parse the EDID, correct? It also notifies about the jack status. Hence, if there the cable is disconnected the application will know and act accordingly. Is this understanding correct?
Correct.
Also, I see that hda_pcm_ops does not have a trigger or start/stop functions, how does it know when to start/stop audio. Maybe with azx_pcm_trigger?
The start/stop isn't issued in the driver level because DMA is still working. For HD-audio, it's really just like a normal jack plug/unplug.
Takashi
participants (3)
-
Ricardo Neri -
Stephen Warren -
Takashi Iwai