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Re: [PATCH 16/16] alsa sound support for mips

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH 16/16] alsa sound support for mips
From: Fuxin Zhang <fxzhang@ict.ac.cn>
Date: Wed, 18 Apr 2007 22:13:02 +0800
Cc: tiansm@lemote.com, perex@suse.cz, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, Fuxin Zhang <zhangfx@lemote.com>
In-reply-to: <20070418135412.GG3938@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <11766507661684-git-send-email-tiansm@lemote.com> <117665076617-git-send-email-tiansm@lemote.com> <1176650766907-git-send-email-tiansm@lemote.com> <11766507663301-git-send-email-tiansm@lemote.com> <11766507663039-git-send-email-tiansm@lemote.com> <1176650766685-git-send-email-tiansm@lemote.com> <11766507661790-git-send-email-tiansm@lemote.com> <11766507672298-git-send-email-tiansm@lemote.com> <11766507672043-git-send-email-tiansm@lemote.com> <11766507674145-git-send-email-tiansm@lemote.com> <20070418135412.GG3938@linux-mips.org>
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                vaddr = runtime->dma_area + offset;
+#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)

Please use CONFIG_MIPS instead of __mips__ in #if / #ifdefs.

The question if #ifdefing is the right approach to solve this problem is
something else but I think no, ....
I would agree that it is quite ugly, but changing virt_to_page for it does not seem right either.
+               page = virt_to_page(CAC_ADDR(vaddr));
+#else
                page = virt_to_page(vaddr);
+#endif

So this is needed because the MIPS virt_to_page is returning a unsuitable
value if vaddress is not a KSEG0 (64-bit: cached XKPHYS) address which is
what GFP allocations and the slab will return.  So now we have to deciede
if

 a) the MIPS __pa() should be changed to handle uncached addresses.
 b) the sound code here is simply broken.

Some drivers seem to allocate runtime->dma_area from vmalloc, so this
whole area in the sound code is looking like built on quicksand ...
+#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
+       /* all mmap using uncached mode */
+       area->vm_page_prot = pgprot_noncached(area->vm_page_prot);
+       area->vm_flags |= ( VM_RESERVED | VM_IO);

VM_RESERVED will prevent the buffer from being freed.  I assume that is
another workaround for some kernel subsystem blowing up when being fed a
pointer to an uncached RAM address?  This smells like a memory leak.

Oh, VM_RESERVED should be a memory leak problem, we can remove it.
I don't remember any case of other subsystem's problem, just did not think much
to add those flags.
+#endif
+
        offset = area->vm_pgoff << PAGE_SHIFT;
        switch (offset) {
        case SNDRV_PCM_MMAP_OFFSET_STATUS:
diff --git a/sound/core/sgbuf.c b/sound/core/sgbuf.c
index cefd228..535f0bc 100644
--- a/sound/core/sgbuf.c
+++ b/sound/core/sgbuf.c
@@ -91,12 +91,21 @@ void *snd_malloc_sgbuf_pages(struct device *device,
                }
                sgbuf->table[i].buf = tmpb.area;
                sgbuf->table[i].addr = tmpb.addr;
+#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
+               sgbuf->page_table[i] = virt_to_page(CAC_ADDR(tmpb.area));

VM_RESERVED will prevent the buffer from being freed.  I assume that is
another workaround for some kernel subsystem blowing up when being fed a
pointer to an uncached RAM address?  This smells like a memory leak.

+#else
                sgbuf->page_table[i] = virt_to_page(tmpb.area);
+#endif
                sgbuf->pages++;
        }
sgbuf->size = size;
+#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
+       /* maybe we should use uncached accelerated mode */
+       dmab->area = vmap(sgbuf->page_table, sgbuf->pages, VM_MAP | VM_IO, 
pgprot_noncached(PAGE_KERNEL));
+#else
        dmab->area = vmap(sgbuf->page_table, sgbuf->pages, VM_MAP, PAGE_KERNEL);
+#endif

I would suggest to get rid of this ifdef with a new arch-specific function
like vmap_io_buffer which will do whatever a platform seems fit for this
case?
I think arch-specific function is the correct way, but don't know what the alsa gods think.
        if (! dmab->area)
                goto _failed;
        return dmab->area;

  Ralf





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