Mapping frame buffer memory as uncached

Mapping frame buffer memory as uncached

[Alexei Fedorov]

Hi Ard,


The side effect of the following commit on 6 April:


ArmPlatformPkg/FVP: map motherboard VRAM as uncached memory

The VRAM of the PL111 on the FVP Base/Foundation models is described as
device memory rather than uncached memory, which is not an accurate
description of the nature of the region (i.e., a framebuffer), and may
result in problems when using accelerated string routines to access the
region, since this may legally involve unaligned accesses or DC ZVA
instructions, which are not allowed on device mappings.

So split of the 8 MB VRAM region into a separate region, and map it using
memory attributes.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

is that now frame buffer memory region has Executable attribute set, which can be checked in DS-5 debugger Memory Map tab.

Was this expected?


Thanks.

Alexei.




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Re: Mapping frame buffer memory as uncached

[Ard Biesheuvel]

On 20 December 2017 at 15:17, Alexei Fedorov <Alexei.Fedorov@arm.com> wrote:
> Hi Ard,
>
>
> The side effect of the following commit on 6 April:
>
>
> ArmPlatformPkg/FVP: map motherboard VRAM as uncached memory
>
> The VRAM of the PL111 on the FVP Base/Foundation models is described as
> device memory rather than uncached memory, which is not an accurate
> description of the nature of the region (i.e., a framebuffer), and may
> result in problems when using accelerated string routines to access the
> region, since this may legally involve unaligned accesses or DC ZVA
> instructions, which are not allowed on device mappings.
>
> So split of the 8 MB VRAM region into a separate region, and map it using
> memory attributes.
>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
> Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
> Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
>
> is that now frame buffer memory region has Executable attribute set, which
> can be checked in DS-5 debugger Memory Map tab.
>
> Was this expected?
>

Not for one second. Thanks for the report, I will propose a fix.