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Wed, 10 Jun 2020 11:02:43 -0700 (PDT) Date: Wed, 10 Jun 2020 19:02:41 +0100 From: Lee Jones To: Rob Herring Cc: Michael Walle , Andy Shevchenko , Ranjani Sridharan , david.m.ertman@intel.com, shiraz.saleem@intel.com, Mark Brown , "open list:GPIO SUBSYSTEM" , devicetree , Linux Kernel Mailing List , Linux HWMON List , Linux PWM List , LINUX-WATCHDOG , 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: <20200610180241.GU4106@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: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org On Wed, 10 Jun 2020, Rob Herring wrote: > On Wed, Jun 10, 2020 at 1:19 AM Lee Jones wrote: > > > > 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. > > TBC, while fine for a driver to bind on 'simple-mfd', a DT compatible > with that alone is not fine. 'simple-mfd' essentially means: "This device doesn't do anything useful, but the children do." When used with 'syscon' it means: "Memory for this device is shared between all children" Adding more specific/descriptive compatible strings is conceptually fine, but they should not be forced to bind to a real driver using them. Else we're creating drivers for the sake of creating drivers. This is especially true with 'simple-mfd' is used without 'syscon'. > > > 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. > > > > > - 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. > > I think it is really the syscon mfd driver you want to generalize to > other buses. Though with a quick look at it, there's not really a > whole lot to share. The regmap lookup would be the main thing. You are > going to need a driver instance for each bus type. On it. -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog