netdev - Re: [RFC v5 net-next 01/13] mfd: ocelot: add support for external mfd control over SPI for the VSC7512

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Message-ID: <Yd2JvH/D2xmH8Ry7@sirena.org.uk>
Date:   Tue, 11 Jan 2022 13:44:28 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Colin Foster <colin.foster@...advantage.com>,
        linux-gpio@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>, UNGLinuxDriver@...rochip.com,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [RFC v5 net-next 01/13] mfd: ocelot: add support for external
 mfd control over SPI for the VSC7512

On Tue, Jan 11, 2022 at 10:13:43AM +0000, Lee Jones wrote:

> Unless something has changed or my understanding is not correct,
> regmap does not support over-lapping register ranges.

If there's no caches and we're always going direct to hardware it will
work a lot of the time since the buses generally have concurrency
protection at the lowest level, though if the drivers ever do any
read/modify/write operations the underlying hardware bus isn't going to
know about it so you could get data corruption if two drivers decide to
try to operate on the same register.  If there's caches things will
probably go badly since the cache will tend to amplify the
read/modify/write issues.

> However, even if that is required, I still think we can come up with
> something cleaner than creating a whole API based around creating
> and fetching different regmap configurations depending on how the
> system was initialised.

Yeah, I'd expect the usual pattern is to have wrapper drivers that
instantiate a regmap then have the bulk of the driver be a library that
they call into should work.

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