[PATCH V2 2/2] efi/fb: Convert PCI bus address to resource if translated by the bridge

On 22 June 2018 at 20:30, Sinan Kaya [off-list ref] wrote:

On 6/22/2018 2:01 PM, Ard Biesheuvel wrote:

quoted

quoted

Yes, it is part of the PCI I/O protocol definition. FrameBufferBase is
described as

"""
Base address of graphics linear frame buffer. Info contains
information required to allow software to draw directly to the
frame buffer without using Blt().Offset zero in
FrameBufferBase represents the upper left pixel of the
display.
"""

I just tried AMD Radeon and NVidia graphics cards on a system with
non-1:1 mapped MMIO windows, and in both cases, the GOP protocol
structure is populated correctly, i.e., using the CPU address not the
PCIe address.

EDK2 only recently gained support for MMIO translation in the host
bridge driver, so I so wonder if this is a platform issue rather than
a driver issue. It may be worth a try to dump the results of
GetBarAttributes() of all PCI I/O protocol instances (either in UEFI
or in the stub), to double check that the correct values are returned.

Thanks for checking out other platforms. I'll mark the issue as a BIOS
issue and bounce your feedback to the BIOS provider.

I screwed up my testing, unfortunately. Both the public AMD GOP driver
I tried, and the Nvidia GT218 under x86 emulation break when using
MMIO translation. However, GraphicsOutputDxe in the EDK2 tree gets it
right, and uses PciIo->GetBarAttributes() to get the address of the
framebuffer region, which will return the CPU address not the PCI
address.

Let's hold onto this patch for the moment.

Yes. I'd like to get this resolved as well, but if the drivers are
dereferencing BAR values as CPU addresses, this is unlikely to be the
only thing that is broken under outbound translation.