Re: [Xen-devel] Question about PLATFORM_QUIRK_DOM0_MAPPING_11

[Chen Baozi <baozich@xxxxxxxxx>]

On Sep 3, 2013, at 8:49 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

> On Tue, 2013-09-03 at 20:41 +0800, Chen Baozi wrote:
>> When porting Xen on OMAP5, we need to add .quirks handler which
>> returns the PLATFORM_QUIRK_DOM0_MAPPING_11. I have read the related
>> set_memory_reg() in domain_build.c. And My question is in which case
>> we don't need to return PLATFORM_QUIRK_DOM0_MAPPING_11 in .quirks and
>> how Xen handles that case to populate right P2M to dom0?
> 
> DOM0_MAPPING_11 is a workaround for lack of an iommu, either in hardware
> (e.g. ARM SMMU) or in software (e.g. Stefano's swiotlb patches). In the
> short term it seems like Stefano's patches are going to be ready before
> we have an SMMU driver in the hypervisor.
> 
> In any case DOM0_MAPPING_11 will hopefully go away before too long.

Thanks a lot. And one more question :P

The reason that we cannot boot successfully without DOM0_MAPPING_11 on
OMAP5 is because in that case the physical address dom0 writes to DMA
controller is intermediate physical address rather than physical address.
If we did the 1:1 mapping, the IPA of dom0 is then equal to the PA, in
which case the DMA can work properly in dom0. Is this the right explanation
why we need PLATFORM_QUIRK_DOM0_MAPPING_11 without either SMMU or swiotlb?

Cheers,

Baozi

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