linux-kernel - Re: [PATCH] arm64: dts: qcom: sdm845-db845c: Mark cont splash memory region as reserved

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Date:   Thu, 9 Feb 2023 15:54:53 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        dt <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: sdm845-db845c: Mark cont splash memory
 region as reserved

On 09/02/2023 14:22, Bryan O'Donoghue wrote:
> On 09/02/2023 12:11, Bryan O'Donoghue wrote:
>>> If the bootloader splash is enabled then this memory is used until the
>>> DPU driver instructs MDP5 pipes to suck data from a newly assigned 
>>> address,
>>> so there's a short window where it is.
>>
>> It seems a shame to reserve 30 something megabytes of memory for 
>> continuous splash unless we are actually using it is my point.
>>
>> If I'm running headless its just wasted memory.
> 
> Couldn't we
> 
> 1. Find reserved continuous splash memory
> 2. Fee it in the MDP when we make the transition

Qualcomm has investigated freeing the MDP/DPU cont_splash memory, but I 
fear that the end result was that it is not _that_ easy to free it. It 
is marked as reserved/no-map, so the kernel doesn't think about it as a 
memory region. Adding it back required hacking around that.

-- 
With best wishes
Dmitry