Re: [PATCH edk2-platforms v3 12/17] ARM/VExpressPkg: Allocate framebuffer using EfiRuntimeServicesData

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

On 21 March 2018 at 19:07, Girish Pathak <Girish.Pathak@arm.com> wrote:
>
>
>> -----Original Message-----
>> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
>> Sent: 21 March 2018 03:38
>> To: Girish Pathak <Girish.Pathak@arm.com>
>> Cc: edk2-devel@lists.01.org; Leif Lindholm <leif.lindholm@linaro.org>;
>> Matteo Carlini <Matteo.Carlini@arm.com>; Stephanie Hughes-Fitt
>> <Stephanie.Hughes-Fitt@arm.com>; nd <nd@arm.com>; Arvind Chauhan
>> <Arvind.Chauhan@arm.com>; Daniil Egranov <Daniil.Egranov@arm.com>;
>> Thomas Abraham <thomas.abraham@arm.com>
>> Subject: Re: [PATCH edk2-platforms v3 12/17] ARM/VExpressPkg: Allocate
>> framebuffer using EfiRuntimeServicesData
>>
>> On 21 March 2018 at 00:18, Girish Pathak <girish.pathak@arm.com> wrote:
>> > As per the UEFI specification(2.7) section 12.9, the GOP framebuffer
>> > memory can be accessed in the pre-boot and the post boot phase (by OS)
>> > Therefore the memory type EfiBootServicesData is incorrect for the
>> > framebuffer memory allocation. Change EfiBootServicesData with
>> > EfiRuntimeServicesData flag so that allocated memory can be access by
>> > the OS in the post boot phase.
>> >
>>
>> EfiRuntimeServicesData is intended for allocations that the EFI runtime
>> services need to access themselves at runtime, and will hence be virtually
>> remapped by SetVirtualAddressMap().
>>
>> This does not apply to the framebuffer. Even if it may be used at OS runtime,
>> the firmware itself will never access it, so EfiRuntimeServicesData is not
>> appropriate
>>
>> Please use EfiReservedMemory instead.
>
> Specification (UEFI Spec 2_7_A Sept 6.pdf) describes EfiReservedMemoryType as  Not usable before and after ExitBootServices, See Table 28 & 29
> Hence EfiReservedMemoryType is not suitable in this case.  Agree?
>

It is not usable as ordinary memory, given that you turn it into
'special' memory (with side effects) by turning it into a framebuffer.

So EfiReservedMemory is perfectly appropriate here.