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

[Takashi Iwai <tiwai@suse.de>]

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.

a small concern about GFP_KERNEL is that i experienced the stall when
the kernel tried to allocate large continuous pages with GFP_KERNEL,
e.g. modprobe stops infinitely in the module init phase (and you
cannot even interrupt that process).

does dma_alloc_coherent(GFP_KERNEL) with big pages work without stall?


Takashi


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