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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Fri, 22 Jun 2018 21:29:36 +0200
Message-ID: <CAKv+Gu-bwCFhCKiA7P1amMLeBaSxsjk0d6aPjAr9nCvOBPJA6w@mail.gmail.com>
Subject: Re: [PATCH V2 2/2] efi/fb: Convert PCI bus address to resource if
 translated by the bridge
To:     Sinan Kaya <okaya@codeaurora.org>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        "open list:EFIFB FRAMEBUFFER DRIVER" <linux-fbdev@vger.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        linux-arm-msm@vger.kernel.org, Timur Tabi <timur@codeaurora.org>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:FRAMEBUFFER LAYER" <dri-devel@lists.freedesktop.org>,
        Peter Jones <pjones@redhat.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
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On 22 June 2018 at 20:30, Sinan Kaya <okaya@codeaurora.org> wrote:
> On 6/22/2018 2:01 PM, Ard Biesheuvel wrote:
>>> 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.