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From: Lee Jones <lee.jones@linaro.org>
To: Michael Walle <michael@walle.cc>
Cc: "Andy Shevchenko" <andy.shevchenko@gmail.com>,
	"Ranjani Sridharan" <ranjani.sridharan@linux.intel.com>,
	david.m.ertman@intel.com, shiraz.saleem@intel.com,
	"Rob Herring" <robh+dt@kernel.org>,
	"Mark Brown" <broonie@kernel.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	devicetree <devicetree@vger.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org,
	linux-watchdog@vger.kernel.org,
	"linux-arm Mailing List" <linux-arm-kernel@lists.infradead.org>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Bartosz Golaszewski" <bgolaszewski@baylibre.com>,
	"Jean Delvare" <jdelvare@suse.com>,
	"Guenter Roeck" <linux@roeck-us.net>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Wim Van Sebroeck" <wim@linux-watchdog.org>,
	"Shawn Guo" <shawnguo@kernel.org>, "Li Yang" <leoyang.li@nxp.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Jason Cooper" <jason@lakedaemon.net>,
	"Marc Zyngier" <maz@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller
Date: Wed, 10 Jun 2020 08:56:15 +0100
Message-ID: <20200610075615.GT4106@dell> (raw)
In-Reply-To: <f7b2b690750edd022000ab56d2f58154@walle.cc>

On Wed, 10 Jun 2020, Michael Walle wrote:

> Am 2020-06-10 09:19, schrieb Lee Jones:
> > On Wed, 10 Jun 2020, Michael Walle wrote:
> > > Am 2020-06-09 21:45, schrieb Lee Jones:
> > > > On Tue, 09 Jun 2020, Michael Walle wrote:
> > > > > > We do not need a 'simple-regmap' solution for your use-case.
> > > > > >
> > > > > > Since your device's registers are segregated, just split up the
> > > > > > register map and allocate each sub-device with it's own slice.
> > > > >
> > > > > I don't get it, could you make a device tree example for my
> > > > > use-case? (see also above)
> > > >
> > > >     &i2cbus {
> > > >         mfd-device@10 {
> > > >             compatible = "simple-mfd";
> > > >             reg = <10>;
> > > >
> > > >             sub-device@10 {
> > > >                 compatible = "vendor,sub-device";
> > > >                 reg = <10>;
> > > >             };
> > > >    };
> > > >
> > > > The Regmap config would be present in each of the child devices.
> > > >
> > > > Each child device would call devm_regmap_init_i2c() in .probe().
> > > 
> > > Ah, I see. If I'm not wrong, this still means to create an i2c
> > > device driver with the name "simple-mfd".
> > 
> > Yes, it does.
> > 
> > > Besides that, I don't like this, because:
> > >  - Rob already expressed its concerns with "simple-mfd" and so on.
> > 
> > Where did this take place?  I'd like to read up on this.
> 
> In this thread:
> https://lore.kernel.org/linux-devicetree/20200604211039.12689-1-michael@walle.cc/T/#m16fdba5962069e7cd4aa817582ee358c9fe2ecbf
> 
> > 
> > >  - you need to duplicate the config in each sub device
> > 
> > You can have a share a single config.
> > 
> > >  - which also means you are restricting the sub devices to be
> > >    i2c only (unless you implement and duplicate other regmap configs,
> > >    too). For this driver, SPI and MMIO may be viable options.
> > 
> > You could also have a shared implementation to choose between different
> > busses.
> 
> Then what is the difference between to have this shared config in the
> parent driver only and use the functions which are already there, i.e.
> dev_get_regmap(parent). But see, below, I'll wait with what you're
> coming up.

The difference is the omission of an otherwise pointless/superfluous
driver.  Actually, it's the difference between the omission of 10
pointless drivers!

> > > Thus, I'd rather implement a simple-mfd.c which implement a common
> > > I2C driver for now and populate its children using
> > > devm_of_platform_populate(). This could be extended to support other
> > > type of regmaps like SPI in the future.
> > > 
> > > Also some MFD drivers could be moved to this, a likely candidate is
> > > the smsc-ece1099.c. Although I don't really understand its purpose,
> > > if don't have CONFIG_OF.
> > > 
> > > Judging from the existing code, this simple-mfd.c wouldn't just be
> > > "a list of compatible" strings but also additional quirks and tweaks
> > > for particular devices in this list.
> > 
> > Hold off on the simple-mfd.c idea, as I'm not taken by it yet and
> > wouldn't want you to waste your time.  I have another idea which would
> > help.  Give me a few days to put something together.
> 
> Sure. I'm just glad there is now a discussion about this issue.

It's very much in my mind.

I've been meaning to do something about it for quite some time.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog

  reply index

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04 21:10 [PATCH v4 00/11] Add support for Kontron sl28cpld Michael Walle
2020-06-04 21:10 ` [PATCH v4 01/11] dt-bindings: mfd: Add bindings for sl28cpld Michael Walle
2020-06-09 16:28   ` Rob Herring
2020-06-04 21:10 ` [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller Michael Walle
2020-06-05  6:57   ` Lee Jones
2020-06-05  9:51     ` Michael Walle
2020-06-05 10:50     ` Mark Brown
2020-06-05 20:07       ` Michael Walle
2020-06-06 11:46         ` Mark Brown
2020-06-06 12:45           ` Michael Walle
2020-06-08  8:28             ` Lee Jones
2020-06-08 10:02               ` Andy Shevchenko
2020-06-08 15:41                 ` Michael Walle
2020-06-08 18:56                   ` Lee Jones
2020-06-08 21:09                     ` Michael Walle
2020-06-09  6:47                       ` Lee Jones
2020-06-09 14:38                         ` Michael Walle
2020-06-09 14:42                           ` Mark Brown
2020-06-09 15:01                             ` Michael Walle
2020-06-09 17:15                               ` Rob Herring
2020-06-09 17:29                                 ` Mark Brown
2020-06-09 18:41                                 ` Lee Jones
2020-06-09 15:19                           ` Lee Jones
2020-06-09 15:30                             ` Michael Walle
2020-06-09 19:45                               ` Lee Jones
2020-06-10  7:10                                 ` Michael Walle
2020-06-10  7:19                                   ` Lee Jones
2020-06-10  7:49                                     ` Michael Walle
2020-06-10  7:56                                       ` Lee Jones [this message]
2020-06-10  9:27                                         ` Michael Walle
2020-06-10 18:30                                           ` Lee Jones
2020-06-10 17:16                                     ` Rob Herring
2020-06-10 18:02                                       ` Lee Jones
2020-06-08 18:20                 ` Lee Jones
2020-06-09 16:54               ` Rob Herring
2020-06-09 18:52                 ` Lee Jones
2020-06-05  8:01   ` Andy Shevchenko
2020-06-05  8:02     ` Andy Shevchenko
2020-06-05 10:09     ` Michael Walle
2020-06-05 10:48       ` Andy Shevchenko
2020-06-05 11:51         ` Michael Walle
2020-06-04 21:10 ` [PATCH v4 03/11] irqchip: add sl28cpld interrupt controller support Michael Walle
2020-06-05  1:26   ` kernel test robot
2020-06-05  8:07   ` Andy Shevchenko
2020-06-08 15:12   ` kernel test robot
2020-06-04 21:10 ` [PATCH v4 04/11] watchdog: add support for sl28cpld watchdog Michael Walle
2020-06-05  8:14   ` Andy Shevchenko
2020-06-05 10:24     ` Michael Walle
2020-06-05 10:50       ` Andy Shevchenko
2020-06-05 13:52         ` Guenter Roeck
2020-06-05 14:09           ` Andy Shevchenko
2020-06-05 15:05             ` Guenter Roeck
2020-06-05 16:04               ` Andy Shevchenko
2020-06-05 16:34                 ` Guenter Roeck
2020-06-04 21:10 ` [PATCH v4 05/11] pwm: add support for sl28cpld PWM controller Michael Walle
2020-06-05  8:15   ` Andy Shevchenko
2020-06-05  8:49   ` Lee Jones
2020-06-05  9:33     ` Andy Shevchenko
2020-06-05 11:39     ` Michael Walle
2020-06-05 18:17     ` Michael Walle
2020-06-08  7:46       ` Lee Jones
2020-06-04 21:10 ` [PATCH v4 06/11] gpio: add support for the sl28cpld GPIO controller Michael Walle
2020-06-05 12:00   ` Andy Shevchenko
2020-06-05 12:42     ` Michael Walle
2020-06-05 13:15       ` Andy Shevchenko
2020-06-05 18:44         ` Michael Walle
2020-06-05 21:19           ` Andy Shevchenko
2020-06-04 21:10 ` [PATCH v4 07/11] hwmon: add support for the sl28cpld hardware monitoring controller Michael Walle
2020-06-05 12:06   ` Andy Shevchenko
2020-06-04 21:10 ` [PATCH v4 08/11] arm64: dts: freescale: sl28: enable sl28cpld Michael Walle
2020-06-04 21:10 ` [PATCH v4 09/11] arm64: dts: freescale: sl28: map GPIOs to input events Michael Walle
2020-06-04 21:10 ` [PATCH v4 10/11] arm64: dts: freescale: sl28: enable LED support Michael Walle
2020-06-04 21:10 ` [PATCH v4 11/11] arm64: dts: freescale: sl28: enable fan support Michael Walle
2020-06-05  6:13 ` [PATCH v4 00/11] Add support for Kontron sl28cpld Lee Jones

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