At Fri, 25 Mar 2011 21:23:26 +1100, Benjamin Herrenschmidt wrote: > > On Fri, 2011-03-25 at 11:12 +0100, Takashi Iwai wrote: > > At Fri, 25 Mar 2011 20:15:33 +1100, > > Benjamin Herrenschmidt wrote: > > > > > > > > We > > > > > must also make sure we don't go down that path for vmalloc memory > > > > > though. > > > > > > > > Yes. > > > > > > I haven't actually checked, but I assume that the test > > > > > > substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV > > > > > > In snd_pcm_default_mmap() takes care of that, please correct me if > > > I'm wrong in which case we'll need something else there. > > > > Well, in the case of usb-audio, it's not handled via > > dma_mmap_coherent(), as the page isn't allocated via > > dma_alloc_coherent() but vmalloc(). > > Right, I just wanted to make sure I was right to assume that a page > allocated by vmalloc() was going to fail the above test in > snd_pcm_default_mmap() and thus -not- get into dma_mmap_coherent()... > just double checking as I'm not totally familiar with the intricacies of > the pcm code :-) > > > The bad commit was to overcome some problems on SH platform, IIRC, > > when it's used with dmix -- i.e. concurrent accesses on the mmapped > > buffer from multiple processes. But, this looks obviously like a > > wrong approach. > > Is this a vivt architecture ? Maybe enforcing some restrictions on the > virtual addresses so they hit the same cache congruence classes ? Possibly, yes. But we need to re-test the problem first with the recent kernel. > > Actually, the buffer allocated there in usb-audio is an intermediate > > buffer, that isn't directly transferred to hardware. We may need a > > bit more consideration what is the best way to solve that issue (if > > it's still really present). > > Right. I wouldn't expect vmalloc stuff to hit HW in most cases anyways, > though I do wonder why you don't pass the buffer directly to the HCD and > avoid that intermediate step but that's a completely different > question :-) The direct buffer was used partly in the older versions. But there was a problem in the accuracy of the buffer playback position, so this was switched to full double-buffering. thanks, Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
