On Sun, 06 Jun 2021 11:18:35 +0200, Takashi Sakamoto wrote: > > Hi, > > All of drivers in ALSA firewire stack processes two chances to process > isochronous packets in any isochronous context; in software IRQ context > for 1394 OHCI, and in process context of ALSA PCM application. > > In the process context, callbacks of .pointer and .ack are utilized. The > callbacks are done by ALSA PCM core under acquiring lock of PCM substream, > > In design of ALSA PCM core, call of snd_pcm_period_elapsed() is used for > drivers to awaken user processes from waiting for available frames. The > function voluntarily acquires lock of PCM substream, therefore it is not > called in the process context since it causes dead lock. As a workaround > to avoid the dead lock, all of drivers in ALSA firewire stack uses > workqueue to delegate the call. > > This patchset is my attempt for the issue. A variant of > 'snd_pcm_period_elapsed()' without lock acquisition is going to be added, > named 'snd_pcm_period_elapsed_without_lock()'. This is used in callbacks > of .pointer and .ack of snd_pcm_ops structure. > > The patchset is still under my test, but it looks to work well in my > easy and rough test. Before posting for merge, I'd like to get your > comment to the idea. When evaluating, please merge below two histories: > * 64584f329352 (for-next) > * 9981b20a5e36 (for-linus) > > Takashi Sakamoto (3): > ALSA: pcm: add snd_pcm_period_elapsed() variant without acquiring lock > of PCM substream > ALSA: firewire-lib: queue event of period elapse in process context > ALSA: firewire-lib: obsolete workqueue for period update The idea is fine, but moving snd_pcm_period_elapsed() as inline static doesn't give much benefit, IMO. Although it can avoid an exported symbol, its cost is much higher, since it'd expand the code at each place of snd_pcm_period_elapsed(), i.e. almost in all driver code. Just provide two exported functions instead in a more straightforward way. thanks, Takashi
