Message-ID: <5de219e973e9d3c1455f1a09b4ce4177@walle.cc>
Date:   Tue, 28 Jul 2020 10:27:11 +0200
From:   Michael Walle <michael@...le.cc>
To:     Lee Jones <lee.jones@...aro.org>
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

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.

>> > >    driver will have a "select MFD_SIMPLE_MFD_I2C". Instead added
>> > >    a small description to the driver itself.
>> > >  - removed "struct simple_mfd_i2c_config" and use regmap_config
>> > >    directly
>> > >  - changed builtin_i2c_driver() to module_i2c_driver(), added
>> > >    MODULE_ boilerplate
>> > >  - cleaned up the included files
>> > >
>> > > Changes since v4:
>> > >  - new patch. Lee, please bear with me. I didn't want to delay the
>> > >    new version (where a lot of remarks on the other patches were
>> > >    addressed) even more, just because we haven't figured out how
>> > >    to deal with the MFD part. So for now, I've included this one.
>> > >
>> > >  drivers/mfd/Kconfig          |  5 ++++
>> > >  drivers/mfd/Makefile         |  1 +
>> > >  drivers/mfd/simple-mfd-i2c.c | 55
>> > > ++++++++++++++++++++++++++++++++++++
>> > >  3 files changed, 61 insertions(+)
>> > >  create mode 100644 drivers/mfd/simple-mfd-i2c.c
>> > >
>> > > diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>> > > index 33df0837ab41..c08539c7a166 100644
>> > > --- a/drivers/mfd/Kconfig
>> > > +++ b/drivers/mfd/Kconfig
>> > > @@ -1162,6 +1162,11 @@ config MFD_SI476X_CORE
>> > >  	  To compile this driver as a module, choose M here: the
>> > >  	  module will be called si476x-core.
>> > >
>> > > +config MFD_SIMPLE_MFD_I2C
>> > > +	tristate
>> > > +	depends on I2C
>> > > +	select REGMAP_I2C
>> >
>> > Please provide a full help.
>> 
>> See above.
>> 
>> >
>> > >  config MFD_SM501
>> > >  	tristate "Silicon Motion SM501"
>> > >  	depends on HAS_DMA
>> > > diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
>> > > index a60e5f835283..78d24a3e7c9e 100644
>> > > --- a/drivers/mfd/Makefile
>> > > +++ b/drivers/mfd/Makefile
>> > > @@ -264,3 +264,4 @@ obj-$(CONFIG_MFD_STMFX) 	+= stmfx.o
>> > >  obj-$(CONFIG_MFD_KHADAS_MCU) 	+= khadas-mcu.o
>> > >
>> > >  obj-$(CONFIG_SGI_MFD_IOC3)	+= ioc3.o
>> > > +obj-$(CONFIG_MFD_SIMPLE_MFD_I2C)	+= simple-mfd-i2c.o
>> > > diff --git a/drivers/mfd/simple-mfd-i2c.c
>> > > b/drivers/mfd/simple-mfd-i2c.c
>> > > new file mode 100644
>> > > index 000000000000..45090ddad104
>> > > --- /dev/null
>> > > +++ b/drivers/mfd/simple-mfd-i2c.c
>> > > @@ -0,0 +1,55 @@
>> > > +// SPDX-License-Identifier: GPL-2.0-only
>> > > +/*
>> > > + * A very simple I2C MFD driver
>> >
>> > Simple MFD - I2C
>> 
>> ok.
>> 
>> > > + * The driver enumerates its children and registers a common
>> > > regmap. Use
>> > > + * dev_get_regmap(pdev->dev.parent, NULL) in the child nodes to
>> > > fetch that
>> > > + * regmap instance.
>> >
>> > This driver creates a single register map with the intention for it to
>> > be shared by all sub-devices.  Children can use their parent's device
>> > structure (dev.parent) in order reference it.
>> 
>> Should this be appended or should it replace my paragraph? If its the
>> latter,
>> the "enumeration of the children" is missing.
> 
> If you want to keep that part, try:
> 
> This driver creates a single register map with the intention for it to
> be shared by all sub-devices.  Children can use their parent's device
> structure (dev.parent) in order reference it.
> 
> Once the register map has been successfully initialised, any
> sub-devices represented by child nodes in Device Tree will be
> subsequently registered.
> 
>> > > + * In the future this driver might be extended to support also
>> > > other interfaces
>> > > + * like SPI etc.
>> >
>> > Remove this please.
>> 
>> 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.

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

-michael

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