[alsa-devel] To disable dma_area caching (twice)

[Takashi Iwai]

At Tue, 5 Jun 2012 09:30:03 +0900,
MASAO TAKAHASHI wrote:
> 
> 
> On Fri, 25 May 2012 09:28:33 +0200
> Takashi Iwai <tiwai at suse.de> wrote:
> 
> > At Fri, 18 May 2012 14:18:57 +0900,
> > MASAO TAKAHASHI wrote:
> > > 
> > > Hi everybody.
> > > Please advice me to solve my problem.
> > > 1.  My environment
> > >     Hardware	Alpha-project MS104-SH4AG with SH7764
> > >     kernel		sh-linux-2.6.29
> > >     ALSA driver sh7764-pcm.c developped 
> > >        by  Manuel Lauss <mano at roarinelk.homelinux.net>
> > > 
> > > 2. My problem
> > > 	I am using the above ALSA driver for SH7764 SSI.
> > > 	I have found the runtime->dma_area address refers DMA area
> > > 	via D-cache.
> > > 	So, playback start is too late after executing 
> > >           snd_pcm_writei().
> > > 	Until D-cache writeback is done, sound data stays in D-cache.
> > > 	I want to read and write from/to main memory 
> > > 	without D-cache.
> > > 
> > > 3. My idea to solve this problem
> > >    3-1 change allocating type of DMA area as follows
> > >        	snd_pcm_lib_preallocate_pages_for_all(
> > >             pcm, SNDRV_DMA_TYPE_CONTINUOUS,
> > >             snd_dma_continuous_data(GFP_KERNEL),
> > >             64*1024, 64*1024);
> > > 
> > >        is changed to
> > > 
> > >         snd_pcm_lib_preallocate_pages_for_all(
> > >             pcm, SNDRV_DMA_TYPE_DEV, <----------- here
> > >             snd_dma_continuous_data(GFP_KERNEL),
> > >             64*1024, 64*1024);
> > >         to let dma_addr pointing P2SEG area without caching
> > > 
> > >     3-2 program internal DMA controller start address 
> > >         with dma_addr
> > >    
> > >           ssidma_outl(sd, (virt_to_phys)(u32)runtime->dma_addr,
> > >                        SSIRDMADR);
> > > 
> > > 
> > >     3-3 add mmap_data_fault routine
> > >          static int sh7764_mmap_data_fault(    
> > >            structvm_area_struct*area,
> > >            struct vm_fault *vmf)
> > >         {
> > > 	  struct snd_pcm_substream *substream = area->vm_private_data;
> > > 	  struct snd_pcm_runtime *runtime;
> > > 	  unsigned long offset;
> > > 	  struct page * page;
> > > 	  void *vaddr;
> > > 	  size_t dma_bytes;
> > > 	
> > > 	  pr_debug("mmap_data_fault\n");
> > > 	  if (substream == NULL)
> > > 		return VM_FAULT_SIGBUS;
> > > 	  runtime = substream->runtime;
> > > 	  offset = vmf->pgoff << PAGE_SHIFT;
> > > 	  dma_bytes = PAGE_ALIGN(runtime->dma_bytes);
> > > 	  if (offset > dma_bytes - PAGE_SIZE)
> > > 		return VM_FAULT_SIGBUS;
> > > 	  if (substream->ops->page) {
> > > 		page = substream->ops->page(substream, offset);
> > > 		if (!page)
> > > 			return VM_FAULT_SIGBUS;
> > > 	  } else {
> > > 		vaddr = runtime->dma_addr + offset;
> > > 		page = virt_to_page(vaddr);
> > > 	  }
> > > 	get_page(page);
> > > 	vmf->page = page;
> > > 	pr_debug("mmap_data_fault:page = %x\n", (unsigned int)page);
> > > 	return 0;
> > >        }
> > >        static struct vm_operations_struct sh7764_pcm_vm_ops_data =
> > >       {
> > > 	.open =		snd_pcm_mmap_data_open,
> > > 	.close =	snd_pcm_mmap_data_close,
> > > 	.fault =	sh7764_mmap_data_fault,
> > >       };
> > > 
> > >   3-3 add sh7764_pcm_mmap routine
> > >       static int sh7764_pcm_mmap(
> > >         struct snd_pcm_substream *substream,
> > > 	struct vm_area_struct *area)
> > >       {
> > > 	unsigned long	offset;
> > > 	unsigned long	mp;
> > > 	unsigned long	virt;
> > > 	int				map_size;
> > > 	struct page *map, *mapend, *ip;
> > > 	struct snd_pcm_runtime *runtime;
> > > 	int	ret;
> > >       #ifdef pgprot_noncached
> > >         area->vm_page_prot = pgprot_noncached(area->vm_page_prot);
> > >       #endif
> > > 	offset = area->vm_pgoff << PAGE_SHIFT;
> > > 	runtime = substream->runtime;
> > > 	map_size = runtime->dma_bytes;
> > > 	mp = virt_to_phys((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);
> > > 	pr_debug("mmap_count=%u\n", substream->mmap_count);
> > > 	return 0;
> > >     }
> > > 
> > >     static struct snd_pcm_ops sh7764_ssidma_ops = {
> > > 	.open		= sh7764_ssidma_open,
> > > 	.close		= sh7764_ssidma_close,
> > > 	.ioctl		= snd_pcm_lib_ioctl,
> > > 	.hw_params	= sh7764_hw_params,
> > > 	.hw_free	= sh7764_hw_free,
> > > 	.prepare	= sh7764_prepare,
> > > 	.trigger	= sh7764_trigger,
> > > 	.pointer	= sh7764_pos,
> > > 	.mmap		= sh7764_pcm_mmap,
> > >     };
> > >  ------------------------------------------------------------
> > > Sorry, so long contents.
> > > 
> > > My solution is right?
> > > or
> > > Is there any better solution ?
> > 
> > The "right" fix would be to implement a proper dma_mmap_coherent() for
> > SH architecture.  It's found for ARM and some PPC variants, but for
> > neither SH nor MIPS.
> 
> I have a question about your reply.
> 
> Do I need to use snd_pcm_mmap_write instead of snd_pcm_writei to disable dma_area caching ?

It's basically irrelevant.  snd_pcm_writei() could be performed via
mmap depending on your setup, too.


Takashi