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 > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel