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Re: ALSA on MIPS platform

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: ALSA on MIPS platform
From: Songmao Tian <tiansm@lemote.com>
Date: Fri, 03 Aug 2007 21:50:36 +0800
Cc: alsa-devel@alsa-project.org, linux-mips@linux-mips.org, greg@kroah.com, Dajie Tan <jiankemeng@gmail.com>
In-reply-to: <20070802.235606.122255120.anemo@mba.ocn.ne.jp>
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References: <46B03CC0.3090000@lemote.com> <20070802.235606.122255120.anemo@mba.ocn.ne.jp>
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Atsushi Nemoto wrote:
On Wed, 01 Aug 2007 15:56:48 +0800, Songmao Tian <tiansm@lemote.com> wrote:
    The problem is clear:
1. dma_alloc_noncoherent() return a non-cached address, and virt_to_page() need a cached logical addr (Have I named it right?)
2. mmaped dam buffer should be non-cached.

We have a ugly patch, but we want to solve the problem cleanly, so can anyone show me the way?

virt_to_page() is used in many place in mm so making it robust might
affect performance.  IMHO virt_to_page() seems too low-level as DMA
API.

If something like dma_virt_to_page(dev, cpu_addr) which can take a cpu
address returned by dma_xxx APIs was defined, MIPS can implement it
appropriately.

And then pgprot_noncached issues still exist...

---
Atsushi Nemoto




I agree, and I am investigating to implement a dma_map_coherent, but It seems dma_map_coherent doesn't solve all the problem and will change a lot of code:(


dma_virt_to_page can be something like this.

diff --git a/include/asm-mips/page.h b/include/asm-mips/page.h
index b92dd8c..d2ead8a 100644
--- a/include/asm-mips/page.h
+++ b/include/asm-mips/page.h
@@ -181,6 +181,8 @@ typedef struct { unsigned long pgprot; } pgprot_t;
#define virt_to_page(kaddr)    pfn_to_page(PFN_DOWN(virt_to_phys(kaddr)))
#define virt_addr_valid(kaddr)    pfn_valid(PFN_DOWN(virt_to_phys(kaddr)))

+#define dma_virt_to_page(dma_addr) pfn_to_page(PFN_DOWN(virt_to_phys(CAC_ADDR(kaddr))))
+
#define VM_DATA_DEFAULT_FLAGS    (VM_READ | VM_WRITE | VM_EXEC | \
                 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 655094d..5e694dd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -39,6 +39,10 @@ extern int sysctl_legacy_va_layout;
#include <asm/pgtable.h>
#include <asm/processor.h>

+#ifndef dma_virt_to_page
+#define dma_virt_to_page virt_to_page
+#endif
+
#define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))

/*
diff --git a/sound/core/sgbuf.c b/sound/core/sgbuf.c
index cefd228..8b29bfd 100644
--- a/sound/core/sgbuf.c
+++ b/sound/core/sgbuf.c
@@ -91,7 +91,7 @@ void *snd_malloc_sgbuf_pages(struct device *device,
        }
        sgbuf->table[i].buf = tmpb.area;
        sgbuf->table[i].addr = tmpb.addr;
-        sgbuf->page_table[i] = virt_to_page(tmpb.area);
+        sgbuf->page_table[i] = dma_virt_to_page(tmpb.area);
        sgbuf->pages++;
    }


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