Re: [Xen-devel] cubieboard2's sd/mmc driver on xen about DMA read data error

[Julien Grall <julien.grall@xxxxxxxxxx>]

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