Re: ALSA dma_area not utilizing D-cahce

[Paul Mundt <lethal@linux-sh.org>]

On Mon, May 21, 2012 at 11:40:05AM +0900, MASAO TAKAHASHI wrote:
> 
> On Mon, 21 May 2012 11:10:04 +0900
> Paul Mundt <lethal@linux-sh.org> wrote:
> > > +	offset = area->vm_pgoff << PAGE_SHIFT;
> > > +	runtime = substream->runtime;
> > > +	map_size = runtime->dma_bytes;
> > > +	mp = (unsigned long)runtime->dma_addr;
> > > +	map = virt_to_page(mp);
> > > +	mapend = virt_to_page(mp+map_size - 1);
> > > +	for (ip = map; ip <= mapend; ip++){
> > > +		SetPageReserved(ip);
> > > +	}
> > > +	area->vm_ops = &sh7764_pcm_vm_ops_data;
> > > +	area->vm_private_data = substream;
> > > +	area->vm_flags |= VM_IO;
> > > +	ret = io_remap_pfn_range(area, area->vm_start, mp>>PAGE_SHIFT, 
> > > +						area->vm_end - area->vm_start,
> > > area->vm_page_prot);
> > > +	if (ret ){
> > > +		pr_debug("sh7764-pcm.c:remap_pfn_range returned EAGAIN\n");
> > > +		return -EAGAIN;
> > > +	}
> > > +	atomic_inc(&substream->mmap_count);
> > > +	return 0;
> > > +}
> > > +
> > Do you really need this? It looks like you could just use
> > snd_pcm_lib_mmap_iomem() directly.
> Is SetPageReserved() not needed ?
>  
No, VM_IO on the VMA ensures that no one's going to touch the pages. If
we switch to using our own VMA for consistent mapping the consistent DMA
allocator then we would need to take care of it, but this is nothing your
mmap routine needs to worry about.