Re: PWM...

[Sascha Hauer <s.hauer@pengutronix.de>]

On Mon, Jan 20, 2014 at 09:14:46AM +0900, Simon Horman wrote:
> On Sun, Jan 19, 2014 at 09:26:40PM +0100, Arnd Bergmann wrote:
> > On Sunday 19 January 2014, Russell King - ARM Linux wrote:
> > > On Sun, Jan 19, 2014 at 11:11:41AM -0800, Olof Johansson wrote:
> > > > On Sun, Jan 19, 2014 at 11:08 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > 
> > > > Ah, yes, if you add a cell that can be done. There'll still be the
> > > > "dead" first cell that will always be 0, but that's alright.
> > > 
> > > Does it not mean that PWM specifications of:
> > > 
> > >         <&pwm1 0 n> <&pwm2 0 n>
> > > 
> > > would need to be converted to:
> > > 
> > >         <&pwm1 0 n 0> <&pwm2 0 n 0>
> > > 
> > > in every DT file referring to these PWMs - because isn't this just
> > > treated in DT as one single array of values?  (If DT knew how many
> > > were in each specification, we wouldn't need the #foo-cells...)
> > 
> > Right: if you change an existing dts file from #pwm-cells=<2> to
> > #pwm-cells=<3>, that requires changing all references to the pwm
> > controller at the same time. If both the per-soc .dtsi files
> > and the per-board .dts files contain references to the same pwm
> > controller, that can end up in significant work. I have not checked
> > if this is the case for i.MX though.
> 
> Would this change imply that old dtbs would no longer work with new kernels?

Not necessarily. With Lothars patch the driver works with pwm-cells=2
and pwm-cells=3. The only problem is that if you compile an old board
dts with a new SoC dtsi it will silently fail since the pwm-cells
setting doesn't match the atcual cells in the dts.

Sascha

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