[RFC] MFD's relationship with Device Tree (OF)

Frank Rowand frowand.list at gmail.com
Wed Jun 24 17:01:42 EDT 2020

+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 at 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 at 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

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