lkml.org 
[lkml]   [2012]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu_ops for GART/SMMU driver
From
On Thu, Jan 5, 2012 at 9:53 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Thu, Jan 05, 2012 at 09:17:18AM +0200, Hiroshi Doyu wrote:
>> Just for DMA mapping test from MPU side, the following one is used.
>
> This patch is buggy.
>
>> +static void dmaapi_test_map_page(struct device *dev)
>> +{
>> +     struct page *page;
>> +     dma_addr_t dma_addr;
>> +     void *cpu_addr;
>> +
>> +     page = alloc_page(GFP_KERNEL);
>> +     BUG_ON(!page);
>> +
>> +     dma_addr = dma_map_page(dev, page, 0, PAGE_SIZE, DMA_TO_DEVICE);
>> +     BUG_ON(!dma_addr);
>> +
>> +     cpu_addr = kmap(page);
>> +     BUG_ON(!cpu_addr);
>> +     memset(cpu_addr, 0xa5, PAGE_SIZE);
>> +     kunmap(cpu_addr);
>
> The DMA API works like this:
>
> - The CPU owns the page or buffer and can access it.
> - You map the page or buffer.
> - The device owns the page or buffer; the CPU must explicitly access it.

I don't understand what "CPU must __explicitly__ access it" means.

Do you mean that CPU must access the mapped buffer when
it __explicitly__ knows that the access does not cause any side effect?


> - You unmap the page or buffer.
> - The CPU again owns the page/buffer and can access it.
>
> Please respect the DMA API rules.
>
> So.  Once dma_map_page() has returned, you must not kmap() or otherwise
> access the data contained in that page until after you have unmapped it.
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2012-01-09 01:43    [W:0.770 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site