Re: cubieboard2's sd/mmc driver on xen about DMA read data error

[Julien Grall <julien.grall@linaro.org>]

On 02/04/14 08:20, Ian Campbell wrote:
> On Wed, 2014-04-02 at 00:10 +0800, 杜琪 wrote:
>> Hi all,

Hello,

>>       I have got this kernel with mmc driver on cubieboard2 from :
>> https://github.com/jwrdegoede/linux-sunxi.git  (test branch) .
>>       I  have made the Xen's Dom0 configuration according
>> this :http://wiki.xenproject.org/wiki/Mainline_Linux_Kernel_Configs.
>> and the kernel can be booted by Xen4.4.
>>       The question we met is that some CMD can be
>> accepted(CMD7,CMD0 ....) and but some can't(CMD52,CMD5,CMD51).
>>       We have found that the CMD51 is attempted to read the data from
>> SD card to memory through DMA , so we replaced all the dma_ops with
>> xen_dma_ops , where it is in struct "dma_map_ops xen_swiotlb_dma_ops"
>> in arch/arm/xen/mm.c.

Can you give more input? (Xen log, ...) DOM0 has a 1:1 mapping layout, 
so the swiotlb should not change anything.

With the 1:1 mapping, the driver can safely use DMA, can you try to see 
which address is used by the DMA request?

> Do I understand correctly that you have solved the issue by doing this?
> If so then please could you send a patch. The process for submitting a
> patch to Linux is described in Documentation/SubmittingPatches.

Using swiotlb everywhere is just too slow. That's why Stefano took an 
hybrid approach (1:1 mapping + bouncing for foreign pages).

Regards,

-- 
Julien Grall

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