Re: [PATCH] 1/3 Implement generic device DMA mapping support

[Takashi Iwai <tiwai@suse.de>]

At Mon, 01 Mar 2004 18:51:56 +0100,
I wrote:
> 
> At Mon, 1 Mar 2004 17:45:17 +0000,
> Russell King wrote:
> > 
> > On Mon, Mar 01, 2004 at 04:41:00PM +0100, Takashi Iwai wrote:
> > > At Sun, 29 Feb 2004 22:38:20 +0000,
> > > Russell King wrote:
> > > > 
> > > > This is the first shot at this - I've tested it on ARM, covering both
> > > > ISA ALSA devices on a PCI machine, and driver model devices on a non-
> > > > PCI, non-ISA machine.  However, it needs more testing.  Can people
> > > > on alsa-devel please test these patches.
> > > > 
> > > > This patch adds support for the generic device/driver model to ALSA
> > > > for the sole purpose of supporting their DMA mapping functionality.
> > > > 
> > > > This patch changes snd_malloc_sgbuf_pages() to use this dma mapping
> > > > functionality.
> > > 
> > > thanks for the patch.  using struct device is nice for
> > > generalization.
> > > 
> > > after a short glance, the only drawback i found is that you disabled
> > > the single pci page allocation hack for i386.  this was needed to
> > > cover the non-atomic page allocation.
> > > for example, sb live needs to allocate more than 100MB single pages
> > > for the wavetable data.  the allocation with GFP_ATOMIC can fail
> > > easily in such a case, althogh there is enough memory after swapping.
> > > maybe we can leave this function as another...
> > 
> > I think you've assumed that:
> > 
> > +       res = dma_alloc_coherent(dev, PAGE_SIZE << pg, dma, GFP_KERNEL);
> > 
> > in snd_malloc_dev_pages() uses GFP_ATOMIC.  Please look closer.
> 
> ah, yes, then it's fine.  thanks.

i was too fast to confirm that -- it turned out that this doesn't
help.

since dma_alloc_coherent() is just a wrapper to pci_alloc_consistent()
on x86, GFP_KERNEL is ignored.  instead, GFP_ATOMIC is used always.
sigh...

IOW, the large page allocation problem i described doesn't exist (on
x86, at least).  only the GFP_KERNEL allocation of single pages is
missing.


Takashi


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