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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-04-03 at 11:09 +0800, æç wrote:
> Hi there, 

Hi,

Once again: Please don't top post (answer below or interleaved with the
quote text) and please stop posting HTML mails.

http://wiki.xen.org/wiki/Asking_Xen_Devel_Questions#Observe_list_etiquette.

> The kernel works without XEN (We have tested it yesterday.), but it
> failed when works with xen hypervisor.
> 
> 
> We have done some research about the MMC driver. 
> If the command has nothing to do with the data transmission, it will
> work, such as CMD7 and CMD0
> But when there is read or write operation( such as CMD52), the DMA
> module of the MMC controller will be used for the data transmission,
> instead of the DMA module of the CPU.
> 
> 
> Our question is, should the XEN DMA memory map operations supported by
> swiotlib  also work for the DMA module of MMC controller? 

As Julien has explained the 1:1 mapping, which is enabled by default for
dom0 since Xen 4.4 should mean that the swiotlb is not necessary for
dom0 access to the MMC.

The swiotlb is there to handle the case where the address which dom0
sees is not the real hardware address, but the 1:1 mapping ensures that
they are the same.

Looking at your logs I don't see anything of the debug from
sunxi_mmc_irq, if you have enabled debug prints from this driver then I
would expect you should see something. This is certainly something worth
investigating.

There is probably a pretty strong correlation between commands which use
DMA and commands which need an IRQ to complete.

Ian.



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