linux-kernel - Re: [PATCH v2 1/2] arm64: dts: qcom: sdm845: Move reserved-memory to devices

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Date:   Tue, 23 Mar 2021 20:32:22 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     Andy Gross <agross@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH v2 1/2] arm64: dts: qcom: sdm845: Move reserved-memory to
 devices

On Fri 12 Mar 20:35 CST 2021, Konrad Dybcio wrote:

> Hi,
> 
> 
> I'm not sure I can agree. Especially for regions like IPA and
> TZ-reserved, which seem the same on (almost?) all..
> 

Thanks Konrad, I appreciate that.

> 
> Sure, the configuration for various remoteprocs *can* differ based on
> what the vendor decided to go with, but more often than not
> (especially with phones) vendors just take a MTP or CDP design, add a
> screen, couple of cameras and call it their own (you can tell by how
> similar most of them to the original reference designs in DT). While
> this is usually the case with lower-end (so not exactly sdm845)
> devices, it also kinda applies here...
> 

Unfortunately there's not a single memory map for each reference design,
the memory map do change during development based on feature set. I
think we can see this already among the few devices.

> 
> I guess for this one, we should find the lowest common denominator and
> keep the nodes that are in the majority of devices in 845 DTSI and
> only alter them if need be.. For WoA devices that may stray further
> away, you can just add a label to reserved-memory and /delete-node/
> it, so that you can rewrite it cleanly. The proposed approach just
> adds a lot - A LOT - of duplication. It will REALLY bite after more
> people submit 845-based phones, of which there are plenty (4 Xperias,
> a whole lot of Xiaomis, a couple of Samsungs, LGs... need I go on?).
> 

I was hoping to make it easier to reason about the memory map for each
device, but if your right about these incoming devices then I agree that
the duplication isn't worth it.

I'll respin patch 2, to get IPA going on the Yoga C630 and put this
patch on hold until this annoys me again :)

Thank you,
Bjorn