linux-kernel - Re: [PATCH v2] memory: renesas-rpc-if: Fix PHYCNT.STRTIM setting

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Message-ID: <Y9JBfTVqjXZqi1r3@ninjato>
Date:   Thu, 26 Jan 2023 10:01:49 +0100
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     linux-renesas-soc@...r.kernel.org,
        Prabhakar <prabhakar.csengg@...il.com>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] memory: renesas-rpc-if: Fix PHYCNT.STRTIM setting

Hi Krzysztof,

> > I need it because of ".revision". This only applies to "ES1.*",
> > there are "ES2.*" and "ES3.*" around which have the same SoC number.
> > Also, there is usually no version numbering for the IP core. We need to
> > use this scheme in a number of other places already, sadly.
> 
> I did not get whether this is runtime characteristics or it can be
> customized with compatible (just you did not do it)?

We have compatibles per SoC, i.e. "r8a7795". We don't have compatibles
for ES versions, i.e. no "r8a7795-es10" or "r8a7795-es20".

The latter would not be practical. We can't know in advance how many ES
revisions there will be, so we can't prepare DTs accordingly. Updating
later would be also difficult because we are usually not notified if
there is a new ES version. Only if there are problems with it. And which
board is available with which ES version is chaotic^2.

Also, if we update DTs later, old DTBs would not work with newer kernels
(requiring a later added compaible for a new ES version). This all still
ignores that it would be a churn to update for every ES version of every
SoC. We have quite many to support. That's why we use soc_device_match()
for ES versions in many places alreday. It was never a problem so far.

That's my reasoning, probably Geert has something to add. He maintains
the Renesas DT files.

All the best,

   Wolfram

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