linux-kernel - Re: [PATCH RFC] arm64: dts: qcom: sdm845: add framebuffer reserved memory

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Message-ID: <ajsfoahkkw4rbwedkuqmcppg2xjr4gqhmsppajg6njuyxouvso@syrbqmgvxorm>
Date: Tue, 18 Nov 2025 14:54:04 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: david@...t.cz, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Casey Connolly <casey.connolly@...aro.org>
Subject: Re: [PATCH RFC] arm64: dts: qcom: sdm845: add framebuffer reserved
 memory

On Tue, Nov 18, 2025 at 01:26:17PM +0100, Konrad Dybcio wrote:
> On 11/17/25 1:27 PM, David Heidelberg via B4 Relay wrote:
> > From: Casey Connolly <casey.connolly@...aro.org>
> > 
> > Stick it with the other default reserved regions, all sdm845 devices
> > use this address except for cheza.
> > 
> > Signed-off-by: Casey Connolly <casey.connolly@...aro.org>
> > Signed-off-by: David Heidelberg <david@...t.cz>
> > ---
> > What do you think about this proposed change?
> > 
> > I assume QCOM recommends or by default use the default memory region,
> > but as can be seen on cheza or sdm850, it seems that vendor can customize
> > the region, thus it's not guranteed to have it always on the same address.
> > 
> > There are two approaches I see:
> > 1. keep as is defined in each device-tree frambuffer node
> > 2. commonize frambuffer node to sdm845.dtsi and in case of exception
> >    remove the node and definite it in device-tree.
> 
> Generally this carveout is useful only if you use the bootloader-
> initiated framebuffer. Post that, drm/msm allocates its own

Previously carveout could have been used for FB memory, but with the
switch to GPUVM I think we lost that ability.

-- 
With best wishes
Dmitry