Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit
Date:   Sun, 14 Jun 2020 12:26:30 +0200
From:   Michael Walle <michael@walle.cc>
To:     Rob Herring <robh+dt@kernel.org>
Cc:     Lee Jones <lee.jones@linaro.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Robin Murphy <robin.murphy@arm.com>,
        GregKroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [RFC] MFD's relationship with Device Tree (OF)
In-Reply-To: <CAL_JsqK1BfYa2WfHFUwm9MB+aZVF5zehDSTZj0MhjuhJyYXdTA@mail.gmail.com>
References: <20200609110136.GJ4106@dell>
 <CAL_JsqK1BfYa2WfHFUwm9MB+aZVF5zehDSTZj0MhjuhJyYXdTA@mail.gmail.com>
User-Agent: Roundcube Webmail/1.4.5
Message-ID: <0709f20bc61afb6656bc57312eb69f56@walle.cc>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Rob,

Am 2020-06-10 00:03, schrieb Rob Herring:
[..]
> Yes, we should use 'reg' whenever possible. If we don't have 'reg',
> then you shouldn't have a unit-address either and you can simply match
> on the node name (standard DT driver matching is with compatible,
> device_type, and node name (w/o unit-address)). We've generally been
> doing 'classname-N' when there's no 'reg' to do 'classname@N'.
> Matching on 'classname-N' would work with node name matching as only
> unit-addresses are stripped.

This still keeps me thinking. Shouldn't we allow the (MFD!) device
driver creator to choose between "classname@N" and "classname-N".
In most cases N might not be made up, but it is arbitrarily chosen;
for example you've chosen the bank for the ab8500 reg. It is not
a defined entity, like an I2C address if your parent is an I2C bus,
or a SPI chip select, or the memory address in case of MMIO. Instead
the device driver creator just chooses some "random" property from
the datasheet; another device creator might have chosen another
property. Wouldn't it make more sense, to just say this MFD provides
N pwm devices and the subnodes are matching based on pwm-{0,1..N-1}?
That would also be the logical consequence of the current MFD sub
device to OF node matching code, which just supports N=1.

-michael