Re: [PATCH 1/3] dt: pwm: lpc32xx: add description of clocks and #pwm-cells properties

[Sylvain Lemieux <slemieux.tyco@gmail.com>]

Hi Rob,

On Tue, 2017-01-03 at 10:22 -0500, Sylvain Lemieux wrote:
> Hi Rob,
> 
> On Wed, 2016-12-21 at 05:30 +0200, Vladimir Zapolskiy wrote:
> > On 12/10/2016 01:51 AM, Vladimir Zapolskiy wrote:
> > > Hi Rob,
> > > 
> > > On 12/09/2016 11:41 PM, Rob Herring wrote:
> > >> On Mon, Dec 05, 2016 at 03:42:37AM +0200, Vladimir Zapolskiy wrote:
> > >>> NXP LPC32xx SoCs have two simple independent PWM controllers with a single
> > >>> output each, in this case there is no need to specify PWM channel argument
> > >>> on client side, one cell for setting PWM output frequency is sufficient.
> > >>>
> > >>> Another added to the description property 'clocks' has a standard meaning
> > >>> of a controller supply clock, in the LPC32xx User's Manual the clock is
> > >>> denoted as PWM1_CLK or PWM2_CLK clock.
> > >>>
> > >>> Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
> > >>> ---
> > >>>  Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt | 7 +++++++
> > >>>  1 file changed, 7 insertions(+)
> > >>>
> > >>> diff --git a/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt b/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt
> > >>> index 74b5bc5..523d796 100644
> > >>> --- a/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt
> > >>> +++ b/Documentation/devicetree/bindings/pwm/lpc32xx-pwm.txt
> > >>> @@ -3,15 +3,22 @@ LPC32XX PWM controller
> > >>>  Required properties:
> > >>>  - compatible: should be "nxp,lpc3220-pwm"
> > >>>  - reg: physical base address and length of the controller's registers
> > >>> +- clocks: clock phandle and clock specifier pair
> > >>> +- #pwm-cells: should be 1, the cell is used to specify the period in
> > >>> +  nanoseconds.
> > >>
> > >> This use of the cell is a bit odd as the period is s/w config and this 
> > >> would typically be a channel selection or such.
> > > 
> > > this is a classic PWM channel configuration property for PWM consumers
> > > described in DT, for instance PWM frequency for display panel backlight
> > > on boot.
> > > 
> > > I think >90% of PWM controllers with device tree bindings have this
> > > argument in #pwm-cells, from bindings/pwm/pwm.txt :
> > > 
> > >     pwm-specifier typically encodes the chip-relative PWM number and
> > >     the PWM period in nanoseconds.
> > > 
> > > You also may skim through phandle arguments of 'pwms' property,
> > > commonly the second argument is the requested frequency.
> > > 
> > > In this particular case I just drop PWM channel number, because
> > > the LPC32xx PWM controller has a single output channel.
> > > 
> > >> What if I want user specified/changed periods?
> > >>
> > > 
> > > The preset period still can be changed over sysfs in runtime.
> > 
> > Rob, have I managed to answer your questions?
> > 
> > If you accept my clarification, could you please ack the change?
> > 
> > --
> > With best wishes,
> > Vladimir
> > 
> ping
> 
> Sylvain
> 
Can you provide feedback; I think your questions were answered
by Vladimir.

Regards,
Sylvain