Re: [Xen-devel] [RFC v01 0/3] xen/arm: introduce IOMMU driver for OMAP platforms

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 22 Jan 2014, Andrii Tseglytskyi wrote:
> Hi,
> 
> The following patch series is an RFC for possible implementation of simple 
> MMU module,
> which is designed to translate IPA to MA for peripheral processors like GPU / 
> IPU
> for OMAP platforms. Currently on our OMAP platform (OMAP5 panda) we have 3 
> external MMUs
> which need to be handled properly.
> 
> It would be great to get a community feedback - will this be useful for Xen 
> project?
> 
> Let me describe an algorithm briefly. It is simple and straightforward.
> The following simple logic is used to translate addresses from IPA to MA:
> 
> 1. During boot time guest domain creates "pagetable" for external MMU IP.
> Pagetable is a singletone data structure, which is stored in ususal kernel
> heap memory. All memory mappings for corresponding MMU are stored inside it.
> Format of "pagetable" is well defined.
> 
> 2. Guest domain enables peripheral remote processor. As a part of enable 
> sequence
> kernel allocates chunks of heap memory needed for remote processor and stores
> pointers to allocated chunks in already created "pagetable". After it writes
> a physical address of pagetable to MMU configuration register. As result MMU 
> IP
> knows about all allocations, and remote processor can use them directly in its
> software.
> 
> 3. Xen omap mmu driver creates a trap for access to MMU configuration 
> registers.
> It reads a physical address of "pagetable" from MMU register and creates a 
> copy
> of it in own memory. As result - we have two similar configuration data 
> structures -
> first - in guest domain kernel, second - in Xen hypervisor.
> 
> 4. Xen omap mmu driver parses its own copy of pagetable and translate all 
> physical
> addresses to corresponding machine addresses using existing p2m API call.
> After it writes a physical address  of its pagetable (with already translated 
> PA to MA)
> to MMU IP configuration registers and returns control to guest domain.
> 
> As a result - guest domain continues enabling remote processor with it MMU 
> and MMU
> will use new pagetable, modified by Xen omap mmu driver. New pagetable will 
> be used
> directly by MMU IP, and its new structure will be hidden for guest domain 
> kernel,
> it won't know anything about p2m translation.

Why don't you map Dom0 1:1 instead?
If you enabled PLATFORM_QUIRK_DOM0_MAPPING_11 (now enabled by default on
all platforms), all this wouldn't be necessary, right?



> Verified with Xen 4.4-unstable, Linux kernel 3.8 as Dom0, Linux(Android) 
> kernel 3.4 as DomU.
> Target platform OMAP5 panda.
> 
> Thank you for your attention,
> 
> Regards,
> 
> Andrii Tseglytskyi (3):
>   arm: omap: introduce iommu module
>   arm: omap: translate iommu mapping to 4K pages
>   arm: omap: cleanup iopte allocations
> 
>  xen/arch/arm/Makefile     |    1 +
>  xen/arch/arm/io.c         |    1 +
>  xen/arch/arm/io.h         |    1 +
>  xen/arch/arm/omap_iommu.c |  492 
> +++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 495 insertions(+)
>  create mode 100644 xen/arch/arm/omap_iommu.c
> 
> -- 
> 1.7.9.5
> 
> 
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> 

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