Re: System hang when using SetMemoryAttributes

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 25 September 2016 at 20:01, Michael Zimmermann
<sigmaepsilon92@gmail.com> wrote:
> Hi,
>
> which side effects can SetMemoryAttributes have?
> I have a device where setting the framebuffer(which is part of DRAM) to
> EFI_MEMORY_UC makes UEFI hang later on(when already outside the lcd driver).
>
> If I do the same on a memory range allocated with AllocateAnyPages instead
> of AllocateAddress UEFI boots just fine(but ofc, the screen doesn't work).
>
> Unfortunately I don't have UART on that device but I'm sure there's no
> assert because I configured DebugLib to reboot the device in that case -
> which never happens, it's just stuck when the console drivers(TerminalDxe
> etc) initialize later on.
>

Hello Michael,

EFI_MEMORY_WC is more suitable for a framebuffer than EFI_MEMORY_UC,
since the latter does not allow unaligned accesses, so any unaligned
store will crash the system.

Since the framebuffer is in DRAM, I assume the reason for setting the
memory attributes is that the device is not DMA coherent? Could you
perhaps describe the hardware in more detail?

-- 
Ard.