linux-kernel - Re: [RFC/patch 0/2] arm64: boot: dts: qcom: sm8150: enable framebuffer for Surface Duo

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Message-ID: <87czlu4bz7.fsf@kernel.org>
Date:   Sat, 18 Dec 2021 09:17:48 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Gustave Monce <gustave.monce@...look.com>
Subject: Re: [RFC/patch 0/2] arm64: boot: dts: qcom: sm8150: enable
 framebuffer for Surface Duo


Hi Konrad,

Konrad Dybcio <konrad.dybcio@...ainline.org> writes:

> On 17.12.2021 13:57, Felipe Balbi wrote:
>> From: Felipe Balbi <felipe.balbi@...rosoft.com>
>>
>> Hi folks,
>>
>> I'm trying to enable the framebuffer on Microsoft Surface Duo. Looking
>> through some internal docs, it came to my attention that the bootloader
>> will fill up the framebuffer address and size to a memory node names
>> splash_region. Adding the node, I can see the address of the
>> framebuffer. Creating the relevant framebuffer device using
>> simple-framebuffer, I can't see it working. Tried dd if=/dev/urandom
>> of=/dev/fb0 and fb-test. None of which manage to get rid of what's
>> already on the screen, put there by the bootloader (platform Logo).
>>
>> Wondering if any of you have seen a behavior such as this and how did
>> you manage to get framebuffer working on SM8150 (I see at least Sony
>> Xperia has the node).
>>
>> Felipe Balbi (2):
>>   arm64: boot: dts: qcom: sm8150: add a label for reserved-memory
>>   arm64: boot: dts: qcom: surface duo: add minimal framebuffer
>>
>>  .../dts/qcom/sm8150-microsoft-surface-duo.dts | 19 +++++++++++++++++++
>>  arch/arm64/boot/dts/qcom/sm8150.dtsi          |  2 +-
>>  2 files changed, 20 insertions(+), 1 deletion(-)
>
> Hi,
>
>
> this issue is totally unique to the Duo and your bootloader configuration.
>
>
> Gus (CCd, co-author of Lumia 950/XL patches) and I were dissecting
> this precise issue (albeit for a different usecase) and in our testing
> it turned out that XBL likely kills the display stack upon exiting
> Boot Services and jumping to LinuxLoader. This may be a bug that comes
> from the legacy of this device, as exiting Boot Services would be
> rather undesirable in that scenario..

This is very nice background information which I didn't have. Thanks :-)

> One fix would be to ask the bootloader team to look into it and fix it
> from there, otherwise you'd have to bring up the display using the
> DPU1 driver, or perhaps in a third-stage-bootloader (pls don't do it

I'll give DPU1 a shot, thanks for the pointer

> for the sanity of us all :D)

no 3rd stages :-)

-- 
balbi