On Mon, Mar 27, 2017 at 03:12:02PM +0200, Takashi Iwai wrote: > On Mon, 27 Mar 2017 12:29:54 +0200, > Vinod Koul wrote: > > > > On Sat, Mar 25, 2017 at 02:21:13AM +0530, Ughreja, Rakesh A wrote: > > > >> >Are these workarounds needed for the legacy driver? > > > >> >If yes, which chips require it? > > > >> > > > > >> > > > >> Yes, these are needed in legacy driver as well. > > > >> From SKL and BXT onwards, it is needed. > > > > > > > >OK, thanks for confirmation. > > > > > > > >Now, from what I read in the above, is the workaround required *only* > > > >after the interrupt is generated? 20us delay isn't so cheap, and we > > > >tend to inquire PCM positions often. If the workaround is needed only > > > >after the PCM period elapse, we can set some flag in the irq handler > > > >and apply the workaround only when necessary. > > > > > > > > > > Yes, Takashi the workaround is required only in the period elapsed > > > interrupt. In some cases the DMA Position updates are delayed and so > > > when the period elapsed interrupt occurs the wait_for_avail thinks that > > > one period worth of data is not available and so returns only on the > > > next period elapsed interrupt. This creates problem for 2 periods > > > playback/capture streams. > > > > > > So even in the period elapsed interrupt the wait is required only if the > > > position is less than the period boundary. > > > > Hi Takashi, > > > > So we need this for 2 periods when the device is in irq mode. Not for other > > cases. ie SKL_PLUS.. > > Yeah, thanks. I'd cook a couple of patches to do that for the legacy > driver. But I still wonder whether the wait is always needed. > > Judging from the description, does the discrepancy of posbuf read > happen *only* when the DMA position goes across the BD boundary? > Or does it happen at any time? I think it can happen anytime, but the impact is not felt unless we have a 2 period case. The update is in-flight, so read returns a value lesser than period boundary. We will sleep till next period ie next wake, which results in overrun. For more than 2 periods it doesn't impact much as the overrun case should not happen > When you trace, you can see that the apps frequently inquires the > position. So, an unconditional wait should be really avoided. If they enquire after a while then we should be okay, but if they are written nicely with good power behaviour then we may have issue, as writes are typically done after period boundaries. > > > But have you seen any user reports on this till now. > > I've seen some bug reports mentioning about crackling audio capture on > SKL (I forgot URLs). It might be triggered by that. Quiet possible.. -- ~Vinod _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
