Re: [PATCH v3 1/2] tests/avocado: update firmware for sbsa-ref

[Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>]

W dniu 30.06.2024 o 16:37, Ard Biesheuvel pisze:
> On Thu, 20 Jun 2024 at 12:20, Marcin Juszkiewicz
> <marcin.juszkiewicz@linaro.org> wrote:
>>
>> Update firmware to have graphics card memory fix from EDK2 commit
>> c1d1910be6e04a8b1a73090cf2881fb698947a6e:
>>
>>      OvmfPkg/QemuVideoDxe: add feature PCD to remap framebuffer W/C
>>
>>      Some platforms (such as SBSA-QEMU on recent builds of the emulator) only
>>      tolerate misaligned accesses to normal memory, and raise alignment
>>      faults on such accesses to device memory, which is the default for PCIe
>>      MMIO BARs.
>>
>>      When emulating a PCIe graphics controller, the framebuffer is typically
>>      exposed via a MMIO BAR, while the disposition of the region is closer to
>>      memory (no side effects on reads or writes, except for the changing
>>      picture on the screen; direct random access to any pixel in the image).
>>
>>      In order to permit the use of such controllers on platforms that only
>>      tolerate these types of accesses for normal memory, it is necessary to
>>      remap the memory. Use the DXE services to set the desired capabilities
>>      and attributes.
>>
>>      Hide this behavior under a feature PCD so only platforms that really
>>      need it can enable it. (OVMF on x86 has no need for this)
>>
>> With this fix enabled we can boot sbsa-ref with more than one cpu core.
>>
> 
> This requires an explanation: what does the number of CPU cores have
> to do with the memory attributes used for the framebuffer?

I have no idea. Older firmware was hanging on several systems but was 
passing in QEMU tests. After closer looking I noticed that Avocado tests 
run with "-smp 1" and pass.

Checked failing system with "-smp 1" and it worked. In meantime you have 
fixed problem in EDK2.

So yes, updating firmware may look like hiding a bug. Which I do not 
know how to track (I can build and test QEMU, but going into its 
internals is something I never done).