[PATCH v3] efifb: avoid reconfiguration of BAR that covers the framebuffer

[Ard Biesheuvel]

On 22 March 2017 at 19:31, Lukas Wunner <lukas at wunner.de> wrote:
> On Wed, Mar 22, 2017 at 03:30:29PM +0000, Ard Biesheuvel wrote:
>> On UEFI systems, the PCI subsystem is enumerated by the firmware,
>> and if a graphical framebuffer is exposed by a PCI device, its base
>> address and size are exposed to the OS via the Graphics Output
>> Protocol (GOP).
>>
>> On arm64 PCI systems, the entire PCI hierarchy is reconfigured from
>> scratch at boot. This may result in the GOP framebuffer address to
>> become stale, if the BAR covering the framebuffer is modified. This
>> will cause the framebuffer to become unresponsive, and may in some
>> cases result in unpredictable behavior if the range is reassigned to
>> another device.
>
> Hm, commit message seems to indicate the issue is restricted to arm64,
> yet there's no IS_ENABLED(ARM64) to constrain the added code to that arch?
>

True. I am eager to get some x86 coverage for this, since I would
expect this not to do any harm. But I'm fine with making it ARM/arm64
specific in the final version.

>
>> +DECLARE_PCI_FIXUP_HEADER(PCI_ANY_ID, PCI_ANY_ID, efifb_fixup_resources);
>
> Maybe this can be constrained to PCI_BASE_CLASS_DISPLAY?
>

How does one do that with DECLARE_PCI_FIXUP_HEADER?