linux-kernel - Re: [PATCH v6 01/13] mfd: add simple regmap based I2C driver

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Message-ID: <20200728083518.GC2419169@dell>
Date:   Tue, 28 Jul 2020 09:35:18 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Michael Walle <michael@...le.cc>
Cc:     linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v6 01/13] mfd: add simple regmap based I2C driver

On Tue, 28 Jul 2020, Michael Walle wrote:

> Am 2020-07-28 10:15, schrieb Lee Jones:
> > On Tue, 28 Jul 2020, Michael Walle wrote:
> > 
> > > Am 2020-07-28 09:19, schrieb Lee Jones:
> > > > On Sun, 26 Jul 2020, Michael Walle wrote:
> > > >
> > > > > There are I2C devices which contain several different functions but
> > > > > doesn't require any special access functions. For these kind of
> > > > > drivers
> > > > > an I2C regmap should be enough.
> > > > >
> > > > > Create an I2C driver which creates an I2C regmap and enumerates its
> > > > > children. If a device wants to use this as its MFD core driver, it has
> > > > > to add an individual compatible string. It may provide its own regmap
> > > > > configuration.
> > > > >
> > > > > Subdevices can use dev_get_regmap() on the parent to get their regmap
> > > > > instance.
> > > > >
> > > > > Signed-off-by: Michael Walle <michael@...le.cc>
> > > > > ---
> > > > > Changes since v5:
> > > > >  - removed "select MFD_CORE" in Kconfig
> > > > >  - removed help text in Kconfig, we assume that the users of this
> > > >
> > > > That's the opposite of what I asked for.
> > > 
> > > What is the use to describe the symbol, if it is not user selectable?
> > > I'm not aware this is done anywhere in the kernel, am I missing
> > > something?
> > 
> > You mean in menuconfig?
> > 
> > I find 'help's helpful even outside of menuconfig.
> > 
> > Surely I'm not the only one who reads them 'raw'?
> 
> Its already available in the header of the file. But sure, I can
> copy it.

Thanks.

[...]

> > > Why would you remove information about the intention of this driver?
> > > If
> > > someone
> > > looks for a place to implement its SPI/I3C/Slimbus MFD driver this
> > > might
> > > come
> > > in handy.
> > 
> > By all means put something similar in the commit log, but it has no
> > place in the driver itself.  Besides, if we were to add support for
> > SPI, it is likely to be a completely separate/unrelated driver.
> 
> Why would that be another driver? It would be 90% copy paste with
> regmap_init_i2c() replaced by regmap_init_spi() and i2c_driver replaced
> by spi_driver.

We'll investigate options if/when the time comes.  If 'spi_driver' and
'i2c_driver' can *sensibly* co-exist, then that is certainly an option
we can explore.

> But I don't care. I'll remove it.

Please.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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