[alsa-devel] sof/hda rework to share more of patch_hdmi.c logic
Hi Takashi,
I notice you are doing a lot of cleanups to HDA code. Just FYI I'm looking into modifying the SOF Intel backend to use snd-hda-codec-hdmi/patch_hdmi.c for HDMI/DP audio support, i.e. to be able to share this code between snd-hda-intel and SOF Intel (and not using hdac-hdmi).
Let me know if this clashes with something you are already looking into. I have a very rough version up and running, but it still needs some work. If the general idea seems ok to you, I'll continue to work on a RFC patch and send for review.
This will change how HDMI is exposed to user-space with SOF Intel drivers, so we need to be extra careful how this is introduced. But this really seems to be the best way to go to avoid the duplicated maintenance work with two drivers that we now have.
PS Tracked in SOF github as https://github.com/thesofproject/linux/issues/1123
Br, Kai
On Thu, 15 Aug 2019 16:28:02 +0200, Kai Vehmanen wrote:
Hi Takashi,
I notice you are doing a lot of cleanups to HDA code. Just FYI I'm looking into modifying the SOF Intel backend to use snd-hda-codec-hdmi/patch_hdmi.c for HDMI/DP audio support, i.e. to be able to share this code between snd-hda-intel and SOF Intel (and not using hdac-hdmi).
Let me know if this clashes with something you are already looking into. I have a very rough version up and running, but it still needs some work. If the general idea seems ok to you, I'll continue to work on a RFC patch and send for review.
That sounds like a good idea.
Currently I've almost done for HD-audio rework for 5.4, so feel free to go ahead.
This will change how HDMI is exposed to user-space with SOF Intel drivers, so we need to be extra careful how this is introduced. But this really seems to be the best way to go to avoid the duplicated maintenance work with two drivers that we now have.
Agreed. I guess the biggest difference is the handling of the DP-MST. The legacy HD-audio HDMI driver takes a different approach for DP-MST, namely, it chooses dynamically the pin that is connected with a monitor. It's for keeping the compatibility (more or less) with old behavior; the program just needs to open the device that corresponds to the notification via jack ctl without fiddling with other extra routing.
PS Tracked in SOF github as https://github.com/thesofproject/linux/issues/1123
OK, will watch out.
thanks,
Takashi
Hi,
On Thu, 15 Aug 2019, Takashi Iwai wrote:
Kai Vehmanen wrote:
into modifying the SOF Intel backend to use snd-hda-codec-hdmi/patch_hdmi.c for HDMI/DP audio support, i.e. to be able to share this code between snd-hda-intel and SOF Intel (and not using hdac-hdmi).
[..]
This will change how HDMI is exposed to user-space with SOF Intel drivers, so we need to be extra careful how this is introduced. But
Agreed. I guess the biggest difference is the handling of the DP-MST. The legacy HD-audio HDMI driver takes a different approach for DP-MST, namely, it chooses dynamically the pin that is connected with a monitor. It's for keeping the compatibility (more or less) with old behavior; the program just needs to open the device that corresponds to the notification via jack ctl without fiddling with other extra routing.
indeed. I've now got to a point where I have the key functionality in place. And after some reworks, the changes to patch_hdmi.c are pretty minimal, which is very nice (I started with a much more evasive patch).
But, but. The DP-MST handling is indeed iffy. I tried a few approaches, but it is hard to reconcile concept of "backup PCMs" of patch_hdmi.c with concepts of ASoC and ALSA topology, where the PCM and DAIs are supposed to be defined in the topology file. This gets worse with SOF (and any similar usage) which allow you to have arbitrary DSP processing between a PCM and the HDMI/DP DAIs. So this seems like a dead-end.
What I ended up doing was to make a new mode to patch_hdmi.c that limits PCM count to actual converter count (and this is aligned with topology), and still supporting DP-MST by always mapping monitors to a free PCM. I've tested some complex DP-MST scenarios and this seems to work pretty well. The jack detection will still be able to tell which of the PCMs have a monitor detected.
I wonder if this would be an acceptable approach, given the reuse benefits we get. Downsides: - assignment of monitors to PCMs will depend on ELD update ordering - in SOF we need to align PCM numbering scheme in all topologies we convert over to patch_hdmi.c
I did not yet figure out how to toggle the new DP-MST mode in patch_hdmi.c in a nice way, so didn't sent patches to list yet. I'll do that early next week. If you want a sneak preview, I uploaded the series at:
https://github.com/thesofproject/linux/pull/1155
Br, Kai
On Fri, 23 Aug 2019 16:29:40 +0200, Kai Vehmanen wrote:
Hi,
On Thu, 15 Aug 2019, Takashi Iwai wrote:
Kai Vehmanen wrote:
into modifying the SOF Intel backend to use snd-hda-codec-hdmi/patch_hdmi.c for HDMI/DP audio support, i.e. to be able to share this code between snd-hda-intel and SOF Intel (and not using hdac-hdmi).
[..]
This will change how HDMI is exposed to user-space with SOF Intel drivers, so we need to be extra careful how this is introduced. But
Agreed. I guess the biggest difference is the handling of the DP-MST. The legacy HD-audio HDMI driver takes a different approach for DP-MST, namely, it chooses dynamically the pin that is connected with a monitor. It's for keeping the compatibility (more or less) with old behavior; the program just needs to open the device that corresponds to the notification via jack ctl without fiddling with other extra routing.
indeed. I've now got to a point where I have the key functionality in place. And after some reworks, the changes to patch_hdmi.c are pretty minimal, which is very nice (I started with a much more evasive patch).
But, but. The DP-MST handling is indeed iffy. I tried a few approaches, but it is hard to reconcile concept of "backup PCMs" of patch_hdmi.c with concepts of ASoC and ALSA topology, where the PCM and DAIs are supposed to be defined in the topology file. This gets worse with SOF (and any similar usage) which allow you to have arbitrary DSP processing between a PCM and the HDMI/DP DAIs. So this seems like a dead-end.
What I ended up doing was to make a new mode to patch_hdmi.c that limits PCM count to actual converter count (and this is aligned with topology), and still supporting DP-MST by always mapping monitors to a free PCM. I've tested some complex DP-MST scenarios and this seems to work pretty well. The jack detection will still be able to tell which of the PCMs have a monitor detected.
I wonder if this would be an acceptable approach, given the reuse benefits we get. Downsides:
- assignment of monitors to PCMs will depend on ELD update ordering
This is true in anyway for the legacy HD-audio, too.
- in SOF we need to align PCM numbering scheme in all topologies we convert over to patch_hdmi.c
I don't think this can be a problem.
Practically seen, the number of PCMs could be just 3 on Skylake and co, even with DP MST, because i915 can drive only up to 3 monitors. The driver *should* receive the unplug event before the plug event to a new monitor, so hda_detach_hda_pcm() gets called before hda_attach_hda_pcm().
The current patch_hdmi.c implementation is based on the theoretical possibility, and limitation to the reduced PCM streams would work, I suppose.
thanks,
Takashi
I did not yet figure out how to toggle the new DP-MST mode in patch_hdmi.c in a nice way, so didn't sent patches to list yet. I'll do that early next week. If you want a sneak preview, I uploaded the series at:
https://github.com/thesofproject/linux/pull/1155
Br, Kai
On Fri, 23 Aug 2019 16:55:09 +0200, Takashi Iwai wrote:
On Fri, 23 Aug 2019 16:29:40 +0200, Kai Vehmanen wrote:
Hi,
On Thu, 15 Aug 2019, Takashi Iwai wrote:
Kai Vehmanen wrote:
into modifying the SOF Intel backend to use snd-hda-codec-hdmi/patch_hdmi.c for HDMI/DP audio support, i.e. to be able to share this code between snd-hda-intel and SOF Intel (and not using hdac-hdmi).
[..]
This will change how HDMI is exposed to user-space with SOF Intel drivers, so we need to be extra careful how this is introduced. But
Agreed. I guess the biggest difference is the handling of the DP-MST. The legacy HD-audio HDMI driver takes a different approach for DP-MST, namely, it chooses dynamically the pin that is connected with a monitor. It's for keeping the compatibility (more or less) with old behavior; the program just needs to open the device that corresponds to the notification via jack ctl without fiddling with other extra routing.
indeed. I've now got to a point where I have the key functionality in place. And after some reworks, the changes to patch_hdmi.c are pretty minimal, which is very nice (I started with a much more evasive patch).
But, but. The DP-MST handling is indeed iffy. I tried a few approaches, but it is hard to reconcile concept of "backup PCMs" of patch_hdmi.c with concepts of ASoC and ALSA topology, where the PCM and DAIs are supposed to be defined in the topology file. This gets worse with SOF (and any similar usage) which allow you to have arbitrary DSP processing between a PCM and the HDMI/DP DAIs. So this seems like a dead-end.
What I ended up doing was to make a new mode to patch_hdmi.c that limits PCM count to actual converter count (and this is aligned with topology), and still supporting DP-MST by always mapping monitors to a free PCM. I've tested some complex DP-MST scenarios and this seems to work pretty well. The jack detection will still be able to tell which of the PCMs have a monitor detected.
I wonder if this would be an acceptable approach, given the reuse benefits we get. Downsides:
- assignment of monitors to PCMs will depend on ELD update ordering
This is true in anyway for the legacy HD-audio, too.
- in SOF we need to align PCM numbering scheme in all topologies we convert over to patch_hdmi.c
I don't think this can be a problem.
Practically seen, the number of PCMs could be just 3 on Skylake and co, even with DP MST, because i915 can drive only up to 3 monitors. The driver *should* receive the unplug event before the plug event to a new monitor, so hda_detach_hda_pcm() gets called before hda_attach_hda_pcm().
The current patch_hdmi.c implementation is based on the theoretical possibility, and limitation to the reduced PCM streams would work, I suppose.
For more correctness: the patch_hdmi.c implementation actually would work even without the backup PCM streams. The backup PCM streams are there for assuring the compatible behavior for old applications that access to the fixed PCM device (e.g. hw:1,1). But, it's hardly possible to get more than three audio-monitors active in the real scenario, we've almost never seen this necessity.
The actual behavior can be found in the description of commit a76056f2e57e:
When monitor is connected, find a proper PCM for the monitor. When monitor is disconnected, unbind the PCM from the pin.
The binding policy (use Intel platform as example) is: 1. Try to use the legacy pin-pcm mapping for the device entry 0 of the pin. 2. If step 1 fails, try to bind pin to the backup PCMs. For example, on Intel platform, if DP MST is enabled, 5 PCMs will be created. PCM 3, PCM 7, PCM 8 are supposed to be used by device entry 0 of pin 5, pin 6 and pin 7. PCM 9 and PCM 10 are the backup PCMs. 3. If step 2 fails, try to find any PCM to bind to the pin.
Removing the backup streams means the removal of step 2, but the driver will keep working in step 3.
thanks,
Takashi
Hey,
On Fri, 23 Aug 2019, Takashi Iwai wrote:
On Fri, 23 Aug 2019, Takashi Iwai wrote:
The current patch_hdmi.c implementation is based on the theoretical possibility, and limitation to the reduced PCM streams would work, I suppose.
[...]
access to the fixed PCM device (e.g. hw:1,1). But, it's hardly possible to get more than three audio-monitors active in the real scenario, we've almost never seen this necessity.
ack. This does feel very unlikely to be a problem. And one could implement a wait list -> delay PCM attach if all audio converters are taken when the new monitor ELD update happens. Upon next disconnect of an already attached audio enabled monitor, one could check the wait list and hook up monitors to the freed converters. But yeah, at least on i915 I don't see the need for this.
This does raise the question whether we should change the behaviour for the non-DSP HD driver as well...? Tempting, but the risk for breaking apps may be too high.
The actual behavior can be found in the description of commit a76056f2e57e:
When monitor is connected, find a proper PCM for the monitor. When monitor is disconnected, unbind the PCM from the pin. The binding policy (use Intel platform as example) is: 1. Try to use the legacy pin-pcm mapping for the device entry 0 of the pin. 2. If step 1 fails, try to bind pin to the backup PCMs. For example, on Intel platform, if DP MST is enabled, 5 PCMs will be created. PCM 3, PCM 7, PCM 8 are supposed to be used by device entry 0 of pin 5, pin 6 and pin 7. PCM 9 and PCM 10 are the backup PCMs. 3. If step 2 fails, try to find any PCM to bind to the pin.Removing the backup streams means the removal of step 2, but the driver will keep working in step 3.
Yes, I didn't have to actually change this code at all. I just limit the PCM count to number of converters, and the above code works without modifications (and skips (2)). Only problem left is how to change to toggle the different rules for calculing pcm count. Unless we change the behaviour for non-DSP HD driver as well, there needs to be some dynamic configuration of patch_hdmi. Kconfig/module-param won't do, I assume distros want to enable both options with same kernel.
Thanks for the quick response!
Br, Kai
On Fri, 23 Aug 2019 17:55:05 +0200, Kai Vehmanen wrote:
Hey,
On Fri, 23 Aug 2019, Takashi Iwai wrote:
On Fri, 23 Aug 2019, Takashi Iwai wrote:
The current patch_hdmi.c implementation is based on the theoretical possibility, and limitation to the reduced PCM streams would work, I suppose.
[...]
access to the fixed PCM device (e.g. hw:1,1). But, it's hardly possible to get more than three audio-monitors active in the real scenario, we've almost never seen this necessity.
ack. This does feel very unlikely to be a problem. And one could implement a wait list -> delay PCM attach if all audio converters are taken when the new monitor ELD update happens. Upon next disconnect of an already attached audio enabled monitor, one could check the wait list and hook up monitors to the freed converters. But yeah, at least on i915 I don't see the need for this.
This does raise the question whether we should change the behaviour for the non-DSP HD driver as well...? Tempting, but the risk for breaking apps may be too high.
It's a good question. On one hand, it'd be good to clean up a bit, but we never know the use of backup PCM ever happened. No news is a good news, after all.
The actual behavior can be found in the description of commit a76056f2e57e:
When monitor is connected, find a proper PCM for the monitor. When monitor is disconnected, unbind the PCM from the pin. The binding policy (use Intel platform as example) is: 1. Try to use the legacy pin-pcm mapping for the device entry 0 of the pin. 2. If step 1 fails, try to bind pin to the backup PCMs. For example, on Intel platform, if DP MST is enabled, 5 PCMs will be created. PCM 3, PCM 7, PCM 8 are supposed to be used by device entry 0 of pin 5, pin 6 and pin 7. PCM 9 and PCM 10 are the backup PCMs. 3. If step 2 fails, try to find any PCM to bind to the pin.Removing the backup streams means the removal of step 2, but the driver will keep working in step 3.
Yes, I didn't have to actually change this code at all. I just limit the PCM count to number of converters, and the above code works without modifications (and skips (2)). Only problem left is how to change to toggle the different rules for calculing pcm count. Unless we change the behaviour for non-DSP HD driver as well, there needs to be some dynamic configuration of patch_hdmi. Kconfig/module-param won't do, I assume distros want to enable both options with same kernel.
We can introduce some new flag in struct hda_codec indicating this restriction, and set it in hdac_hda_codec_probe() beforehand.
Or, we may introduce a new Kconfig and disable statically. The new Kconfig may have "depends on SOF=n" or whatever to be sure. Although we have no 100% guarantee as mentioned in the above, this shouldn't be a big problem. Worth for try.
Honestly speaking, I'm not entirely sure which is a better way to go. Both would be fairly small changes.
You can try them out and see which looks saner. I really don't mind either way.
thanks,
Takashi
participants (2)
-
Kai Vehmanen -
Takashi Iwai