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Re: [PATCH 1/5] MIPS: HIGHMEM DMA on noncoherent MIPS32 processors

To: Kevin Cernekee <cernekee@gmail.com>
Subject: Re: [PATCH 1/5] MIPS: HIGHMEM DMA on noncoherent MIPS32 processors
From: Sergei Shtylyov <sshtylyov@mvista.com>
Date: Tue, 07 Sep 2010 13:11:28 +0400
Cc: Ralf Baechle <ralf@linux-mips.org>, dediao@cisco.com, dvomlehn@cisco.com, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org
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Hello.

On 07-09-2010 8:03, Kevin Cernekee wrote:

The MIPS DMA coherency functions do not work properly (i.e. kernel oops)
when HIGHMEM pages are passed in as arguments.  This patch uses the PPC
approach of calling kmap_atomic() with IRQs disabled to temporarily map
high pages, in order to flush them out to memory.

Signed-off-by: Dezhong Diao <dediao@cisco.com>
Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
---
  arch/mips/mm/dma-default.c |  159 ++++++++++++++++++++++----------------------
  1 files changed, 80 insertions(+), 79 deletions(-)

diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
index 469d401..3f23952 100644
--- a/arch/mips/mm/dma-default.c
+++ b/arch/mips/mm/dma-default.c
[...]
@@ -191,8 +231,8 @@ void dma_unmap_single(struct device *dev, dma_addr_t 
dma_addr, size_t size,
        enum dma_data_direction direction)
  {
        if (cpu_is_noncoherent_r10000(dev))
-               __dma_sync(dma_addr_to_virt(dev, dma_addr), size,
-                          direction);
+               __dma_sync(dma_addr_to_page(dev, dma_addr),
+                          (dma_addr & ~PAGE_MASK), size, direction);

   Parens are not needed here.

@@ -277,15 +297,10 @@ EXPORT_SYMBOL(dma_sync_single_for_cpu);
  void dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle,
        size_t size, enum dma_data_direction direction)
  {
-       BUG_ON(direction == DMA_NONE);
-
        plat_extra_sync_for_device(dev);
-       if (!plat_device_is_coherent(dev)) {
-               unsigned long addr;
-
-               addr = dma_addr_to_virt(dev, dma_handle);
-               __dma_sync(addr, size, direction);
-       }
+       if (!plat_device_is_coherent(dev))
+               __dma_sync(dma_addr_to_page(dev, dma_handle),
+                          (dma_handle & ~PAGE_MASK), size, direction);

   Here as well...

WBR, Sergei

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