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Wed, 10 Jun 2020 11:30:55 -0700 (PDT) Date: Wed, 10 Jun 2020 19:30:53 +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: <20200610183053.GV4106@dell> References: <20200609064735.GH4106@dell> <32287ac0488f7cbd5a7d1259c284e554@walle.cc> <20200609151941.GM4106@dell> <95e6ec9bbdf6af7a9ff9c31786f743f2@walle.cc> <20200609194505.GQ4106@dell> <3a6931248f0efcaf8efbb5425a9bd833@walle.cc> <20200610071940.GS4106@dell> <20200610075615.GT4106@dell> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org On Wed, 10 Jun 2020, Michael Walle wrote: > Am 2020-06-10 09:56, schrieb Lee Jones: > > 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! > > If you want to omit anything generic in the device tree - and as far as > I understand it - that should be the way to go, the specific compatible > string of the parent device has to go somewhere. Thus I'd appreciate > a consolidated (MFD) driver which holds all these, as you say it > pointless drivers. > Because IMHO they are not pointless, rather they are > the actual drivers for the MFD. Its sub nodes are just an implementation > detail to be able to use the OF bindings > (like your clock example or > a phandle to a PWM controller). Just because it is almost nothing there > except the regmap instantiation doesn't mean it is not a valid MFD driver. A valid MFD driver is whatever we (the Linux community at large) define it to be. An MFD is not a real thing. We made it up. It's MFD which is the implementation detail, not the child devices. If a driver a) does very little, and b) the very little it does do can be resolved in a different way, is not a valid driver. It's a waste of disk space. > And there is also additional stuff, like clock enable, version checks, etc. As more functionality is added *then* we can justify a driver. -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog