On Jul 24, 2013, at 5:27 PM, "Tian, Feng" <[email protected]> wrote:
> Hi, Eugene
>
> The EDKII XhciDxe driver doesn’t use PciIo.AllocateBuffer()/Map() to allocate
> DMA buffers. It’s mainly because EDKII is 1:1 mapping on Pci physical address
> and Cpu logical address for IA architecture. AllocateBuffer() is enough for
> current case.
>
So as long as code runs an edk2 Intel/AMD CPU system it does not need to follow
the UEFI spec? So if you had a uninitialized variable or a buffer that was just
a random memory address you would not fix it if you were lucky and it worked on
an edk2 Intel/AMD test system?
> We only implement this feature at EHCI driver as Andrew from Apple was trying
> to use this driver at an ARM based board “Beagle Board”.
>
> For which buffers to be mapped, I think all MMIO buffers specified in XHCI
> spec are required. For how to do this, please refer to EhciDxe driver.
>
> We ever constructed an non 1:1 mapping env at DUET, we mapped 0~1M to
> FFF00000~FFFFFFFF, other memory regions are shifted downwards with 1M offset.
> You can try this way.
>
This is a violation of the UEFI 2.4 (all the way back to EFI 1.10)
specification. Seems like we need to add an SCT for this.... Since folks seem
to confuse passing the SCTs with following the spec.
At a minimum you should update the comments in the driver to tell people that
this is not a UEFI 2.4 (or even EFI 1.10) compatible driver.
2.6.3 Driver-Specific Elements:
12. If a driver is written for a PCI root bridge, then the
EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL and the EFI_PCI_IO_PROTOCOL must be
implemented.
The driver needs to use the DMA scheme defined in the EFI_PCI_IO_PROTOCOL, it
is not legal for a driver to makeup its own way to do DMA.
Thanks,
Andrew Fish
> Thanks
> Feng
>
> From: Cohen, Eugene [mailto:[email protected]]
> Sent: Thursday, July 25, 2013 4:29 AM
> To: [email protected]
> Subject: [edk2] XHCI DMA Buffer Issues
>
> Dear XhciDxe Maintainer,
>
> I’m currently reviewing the XhciDxe driver and I’m trying to figure out how
> DMA buffers are allocated. I see a number of pool and page allocations but I
> do not see any called to PCI_IO Map()/Unmap() or to
> AllocateBuffer()/FreeBuffer().
>
> This appears to be violating the rules for PCI DMA buffers since they are not
> being mapped (and if common buffers are desired then they are also not being
> allocated with AllocateBuffer as required).
>
> Can someone more familiar with XHCI help me determine which buffers need to
> be mapped and how (BusMasterRead, BusMasterWrite, CommonBuffer)?
>
> It would be useful if we had a test environment that could catch driver DMA
> buffer mapping issues earlier. I think one way to do this would be set up
> the MMU in a non-identity mode so that anyone trying to use a processor
> virtual address for DMA would see a failure.
>
> Thanks,
>
> Eugene
>
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