Re: An driver error when I using aplay!

[Takashi Iwai <tiwai@suse.de>]

At Mon, 7 Jun 2004 16:18:12 +0100,
Russell King wrote:
> 
> > No, the problematic line is:
> > 
> > 	WARN_ON(chan->tx_substream != substream);
> > 
> > It can't pass because chan->tx_substream is always NULL (as you wrote)
> > unless hw_params is called.  The check is wrong.
> 
> Ah, well, in my current version of this, I've completely removed that
> check.  Whether there are any other changes, I've no idea.

I also won't debug this any more unless the code is opened
publicly...

>   However,
> my current version doesn't work at all at the moment because its in
> the middle of having experimental DMA support added, rather than
> being sucky PIO-only.

Where we're here:  I'd really like to fix the DMA problem of ALSA on
ARM.  As I sent you before, the patch is already there but I have no
idea whether it's really right or not.  Could you please comment
whether the assumptions below are correct?

- the page struct can be retrieved from dma_addr_t of
  dma_alloc_coherent() like

	virt_to_page(bus_to_virt(addr))

- adding pgprot_noncached() in fop->mmap callback assures that the
  mmaped page is accessed without cache side effects.


thanks,

Takashi


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