Re: [PATCH] ALSA update [6/10] - 2002/07/20

Jaroslav Kysela (perex@suse.cz)
Sun, 29 Sep 2002 22:34:51 +0200 (CEST)


On Sun, 29 Sep 2002, Jeff Garzik wrote:

> Jaroslav Kysela wrote:
> > On 29 Sep 2002, Arjan van de Ven wrote:
> >>what is wrong with the PCI DMA API that makes ALSA wants a private
> >>interface/implementation ?
> >
> >
> > These lines (i386 arch):
> >
> > if (hwdev == NULL || ((u32)hwdev->dma_mask != 0xffffffff))
> > gfp |= GFP_DMA;
> > ret = (void *)__get_free_pages(gfp, get_order(size));
> >
> > Note that some of soundcards have various PCI DMA transfer limits
> > (dma_mask is not set to use full 32-bits). In this case, restricting this
> > hardware to allocate these buffers in first 16MB is not a very good idea.
> > Thus, we have own hacks to allocate memory in whole hardware area.
>
> It sounds like it would be reasonable to fix the ia32 arch code, would
> it not?

We have simple method in our hack:

- try to allocate memory anywhere
- try to allocate memory with GFP DMA if first step fails

Here is updated pci-dma.c code for comments:

===== pci-dma.c 1.8 vs edited =====
--- 1.8/arch/i386/kernel/pci-dma.c Thu May 9 19:24:12 2002
+++ edited/pci-dma.c Sun Sep 29 22:26:46 2002
@@ -19,14 +19,24 @@
void *ret;
int gfp = GFP_ATOMIC;

- if (hwdev == NULL || ((u32)hwdev->dma_mask != 0xffffffff))
+ if (hwdev == NULL || (u32)hwdev->dma_mask <= 0x00ffffff)
gfp |= GFP_DMA;
ret = (void *)__get_free_pages(gfp, get_order(size));

- if (ret != NULL) {
- memset(ret, 0, size);
- *dma_handle = virt_to_phys(ret);
+ if (ret == NULL)
+ return NULL;
+
+ /* try to allocate area in first 16MB memory */
+ if ((gfp & GFP_DMA) == 0 && (u32)hwdev->dma_mask != 0xffffffff &&
+ ((virt_to_phys(ret) + size - 1) & ~(u32)hwdev->dma_mask) != 0) {
+ free_pages(ret, get_order(size));
+ ret = (void *)__get_free_pages(gfp | GFP_DMA, get_order(size));
+ if (ret == NULL)
+ return NULL;
}
+
+ memset(ret, 0, size);
+ *dma_handle = virt_to_phys(ret);
return ret;
}

Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project http://www.alsa-project.org
SuSE Linux http://www.suse.com

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