linux-kernel - Re: [RFC] MFD's relationship with Device Tree (OF)

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Message-ID: <0e9e25cc-b3f2-926a-31dd-c6fafa7d581b@gmail.com>
Date:   Wed, 24 Jun 2020 16:01:42 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Michael Walle <michael@...le.cc>, Rob Herring <robh+dt@...nel.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Mark Brown <broonie@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        GregKroah-Hartman <gregkh@...uxfoundation.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [RFC] MFD's relationship with Device Tree (OF)

+Frank (me)

On 2020-06-22 16:03, Michael Walle wrote:
> Am 2020-06-14 12:26, schrieb Michael Walle:
>> 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.
>>
> 
> Rob? Lee?
> 
> -michael