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Wed, 10 Jun 2020 00:56:17 -0700 (PDT) Date: Wed, 10 Jun 2020 08:56:15 +0100 From: Lee Jones To: Michael Walle Cc: Andy Shevchenko , Ranjani Sridharan , david.m.ertman@intel.com, shiraz.saleem@intel.com, Rob Herring , Mark Brown , "open list:GPIO SUBSYSTEM" , devicetree , Linux Kernel Mailing List , linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-arm Mailing List , Linus Walleij , Bartosz Golaszewski , Jean Delvare , Guenter Roeck , Thierry Reding , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Wim Van Sebroeck , Shawn Guo , Li Yang , Thomas Gleixner , Jason Cooper , Marc Zyngier , Greg Kroah-Hartman , Andy Shevchenko Subject: Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller Message-ID: <20200610075615.GT4106@dell> References: <20200608185651.GD4106@dell> <32231f26f7028d62aeda8fdb3364faf1@walle.cc> <20200609064735.GH4106@dell> <32287ac0488f7cbd5a7d1259c284e554@walle.cc> <20200609151941.GM4106@dell> <95e6ec9bbdf6af7a9ff9c31786f743f2@walle.cc> <20200609194505.GQ4106@dell> <3a6931248f0efcaf8efbb5425a9bd833@walle.cc> <20200610071940.GS4106@dell> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org 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