linux-kernel - Re: [PATCH 03/17] ARM: dts: r8a7742: Add I2C and IIC support

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Message-ID: <20200522201727.GA21376@ninjato>
Date:   Fri, 22 May 2020 22:17:27 +0200
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Jens Axboe <axboe@...nel.dk>, Rob Herring <robh+dt@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "David S. Miller" <davem@...emloft.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>, linux-ide@...r.kernel.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Watchdog Mailing List <linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH 03/17] ARM: dts: r8a7742: Add I2C and IIC support


> > According to the Hardware User's Manual Rev. 1.00, the registers do exist
> > on all RZ/G1, except for RZ/G1E (see below).
> >
> >    "(automatic transmission can be used as a hardware function, but this is
> >     not meaningful for actual use cases)."
> >
> > (whatever that comment may mean?)

Strange comment, in deed. Given the paragraph before, I would guess Gen1
maybe had a "fitting" PMIC where SoC/PMIC handled DVFS kind of magically
with this automatic transfer feature? And Gen2 has not.

> > On R-Car E3 and RZ/G2E, which have a single IIC instance, we
> > handled that by:
> >
> >         The r8a77990 (R-Car E3) and r8a774c0 (RZ/G2E)
> >         controllers are not considered compatible with
> >         "renesas,rcar-gen3-iic" or "renesas,rmobile-iic"
> >         due to the absence of automatic transmission registers.

From a "describe the HW" point of view, this still makes sense to me.
Although, it is unlikely we will add support for the automatic
transmission feature (maybe famous last words).

> > On R-Car E2 and RZ/G1E, we forgot, and used both SoC-specific and
> > family-specific compatible values.

Okay, but we can fix DTs when they have bugs, or?


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