On Fri, May 14, 2010 at 1:39 PM, pl bossart <bossart.nospam at gmail.com> wrote: >> AFAIU, the only issue is lack of ability to fine-tune period size of >> DMA runtime. >> Otherwise, for the requirement, having period-size almost equal >> to ring-buffer serves better than disabling interrupts and using timer >> based updating, more so for VMs with inaccurate timer source. >> >> Then I think, rather then providing a way to disable hw-intr, we'd >> better provide >> a way to modify runtime period-size at DMA Driver level, and >> snd_pcm_period_elapsed seems already capable to handle that. >> That way, disabled interrupts would just be a special case with >> period-size := ULONG_MAX. > > Is this a realistic option? We have to see as it is certainly a more desirable solution. > With the majority of existing hardware > period interrupts are programmed with a flag set in a descriptor when > the DMA linked list is created. That includes HDAudio and numerous > others. I am skeptical that one could reliably modify these > descriptors at run-time, specifically in the case where the controller > caches the descriptors. As we all understand, the requirement is expected to be met only by some h/w that has the capability. Among those candidates, cards that don't support period resize may respond only to "period-size := ULONG_MAX" (i.e interrupt disabling), while more flexible cards can exploit the period-resize feature. Also, let us not forget that almost every embedded device use general purpose DMA that can be re-programmed for different period-size without much trouble.
