Hi, On Sun, Jun 06, 2021 at 12:20:57PM +0200, Takashi Iwai wrote: > 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 for your positive comment. I agree with it. When adding parameters for function internal, we will discuss about the inlining for variations of kernel API again, I guess. After merging for-linus branch into for-next branch, I'm going to post it again. At the time, I may finish enough test. Thanks Takashi Sakamoto
