On Wed, 18 Apr 2007 22:13:02 +0800, Fuxin Zhang <fxzhang@xxxxxxxxx> wrote: > >> +#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT) > >> + /* all mmap using uncached mode */ > >> + area->vm_page_prot = pgprot_noncached(area->vm_page_prot); > >> + area->vm_flags |= ( VM_RESERVED | VM_IO); > >> > > > > VM_RESERVED will prevent the buffer from being freed. I assume that is > > another workaround for some kernel subsystem blowing up when being fed a > > pointer to an uncached RAM address? This smells like a memory leak. > > > > > Oh, VM_RESERVED should be a memory leak problem, we can remove it. > I don't remember any case of other subsystem's problem, just did not > think much > to add those flags. I think pgprot_noncached() is needed because user mapping for a DMA buffer (runtime->dma_area) should be uncache. If so, doing this in snd_pcm_mmap() looks a bit suspicious. It seems snd_pcm_mmap_data() is a place to do such an adjustment. But for now, both snd_pcm_mmap_status() and snd_pcm_mmap_control() returns -ENXIO for MIPS so this is not a real problem. And I wonder if VM_IO is really needed. The area is a DMA buffer, _not_ a memory mapped IO area, isn't it? > > I would suggest to get rid of this ifdef with a new arch-specific function > > like vmap_io_buffer which will do whatever a platform seems fit for this > > case? > > > I think arch-specific function is the correct way, but don't know what > the alsa gods think. JFYI, there were some discussions on this topic a while ago: http://lkml.org/lkml/2006/1/25/117 and I'v seen MIPS version of dma_mmap_coherent(), etc. somewhere... --- Atsushi Nemoto
