[PATCH] pwm: pxa: add device tree support to pwm driver

[mikedunn@newsguy.com (Mike Dunn)]

On 09/04/2013 03:11 PM, Marek Vasut wrote:
>>>

[...]

>>> What's that "secondary PWM" there? I no longer remember, sorry.
>>
>> If pdev->id_entry->driver_data == HAS_SECONDARY_PWM, then pwm_chip->npwm=2
>> when pwmchip_add() is called.  Otherwise pwm_chip->npwm=1.  The driver
>> knows that the second pwm's registers are at a fixed offset from the
>> first.  For compatibility, the pxa27x maps the registers for the third pwm
>> at a distant offset, and makes the offset between 3 and 4 the same as
>> between 1 and 2.  Yes, the driver mkes this unnecessarily complicated. 
>> There should just be one device instance per pwm, and dispense with the
>> whole driver_data thing.  I guess there's some history there.
> 
> OK, I checked the datasheet. The register block for PWM<n + 2> is at offset of 
> 0x10 from PWM<n> , for n in {0, 1} .
> 
> Why can we not just register four PWM blocks, each with 0x10 register window 
> size then? I know there's history (maybe), but then, with DT, this might go 
> away.


Indeed.  That is what I am also thinking.


> 
>>> The question
>>> remains still, we can have two entries there (pxa25x and pxa27x) ORR have
>>> one entry (pxa25x) + mrvl,has-secondary-pwm entry.
>>
>> It looks like defining "compatible" properties that mirror the old
>> platform_device_id names won't fly...
> 
> Yes of course, this won't work. I didn't know the layout exactly.
> 
>> wildcards are verboten (see Sergei's
>> comment).  So your inclination to use one value for the "compatible"
>> property is correct.  I think the way to go is to forget the whole
>> HAS_SECONDARY_PWM in the DT case, have one device instance per pwm, and
>> use "compatible=marvell,pwm". Other suggestions welcome.
> 
> compatbile=marvell,pxa25x-pwm , no ? The lowest CPU with the block.


Unless I am missing something, the compatible string does not need to replicate
any of the existing platform_device_id names, so wouldn't "marvell,pxa" be
better?  Except for register mapping and the number of units present on a
particular pxa variant, the peripheral is software compatible across all pxa
processors.  Plus there is the problem of the 'x' wildcard in "pxa25x-pwm".

Thanks,
Mike