On Wed, 2015-06-24 at 12:41 +0000, Kaskinen, Tanu wrote:
On Tue, 2015-06-23 at 10:06 +0200, Takashi Iwai wrote:
At Tue, 23 Jun 2015 07:51:22 +0000, Kaskinen, Tanu wrote:
(Added pulseaudio-discuss to CC.)
On Mon, 2015-06-22 at 17:44 +0200, Takashi Iwai wrote:
At Mon, 22 Jun 2015 15:21:16 +0000, Kaskinen, Tanu wrote:
On Mon, 2015-06-22 at 14:29 +0100, Liam Girdwood wrote:
<snip>
Tanu, what's your take on the effort for dynamically created PCMs support for pulseaudio ?
It's a significant amount of work, but I think PulseAudio should be improved to support this in any case, if other approaches make life miserable for driver developers.
What would be the interface for getting notifications about new and removed PCM devices? udev?
In general, yes.
PulseAudio (mostly) doesn't use the hw:X devices directly. Instead, it uses logical names like "front", "hdmi", "iec958", etc. Speaking of HDMI specifically, PulseAudio uses devices from "hdmi:X,0" to "hdmi:X,7". With this new dynamic PCM system, do these logical names still work?
Unfortunately, this doesn't work for HDA as is, because of the terribly arcane secret. For keeping the compatibility with the old config, there is a static mapping of the hdmi:x,y and hw:x,z.
Maybe we should introduce a new device class for dynamic HDMI/DP device, something like dhdmi:x,y, to make things straightforward. (Just a concept -- I'm not good at naming.)
Alternatively, we may introduce a new argument to hdmi PCM to access like "hdmi:CARD=x,SYSDEV=y".
What happens if PulseAudio tries to open "dhdmi:x,y" or "hdmi:CARD=x,SYSDEV=y", when y points to a non-HDMI device? If it fails, then PulseAudio can replace its current "hdmi:x,[0-7]" devices with "hdmi:CARD=X,SYSDEV=[0-13]" and blindly try every hw PCM device. But if opening a non-HDMI device through "hdmi:CARD=x,SYSDEV=y" succeeds, then how is PulseAudio supposed to know which hw PCM devices are HDMI devices?
It's a good question. I think this is the core part of the missing pieces.
What I have in my mind is to extend SNDRV_PCM_CLASS_* definition for dedicated to HDMI/DP, e.g. SNDRV_PCM_CLASS_HDMI. The difference between DP and HDMI can be specified in subclass optionally.
Sounds good. Knowing the difference between HDMI, DisplayPort and Thunderbolt would be very nice too. It would enable better labelling in UIs.
I have one minor concern, though: what if a PCM device isn't statically assigned to one output connector? Is it possible that some DSP is able to dynamically change the PCM routing between different outputs? In those cases the PCM class would be useless information (unless there are notifications when the class changes). I don't have any better ideas, though.
This is possible atm, we can route from one PCM to multiple outputs depending on DSP and codec mixer settings. The outputs can even be on different physical interfaces.
Liam