Subject: [PATCH] ARM: dts: lpc32xx: set pwm1 & pwm2 default clock rate

From: [email-masked] (Sylvain Lemieux)
Date: Wed, 05 Oct 2016 10:11:19 -0400

Hi Vladimir,

On Wed, 2016-10-05 at 05:08 +0300, Vladimir Zapolskiy wrote:
> Hi Sylvain,
> 
> On 26.09.2016 21:54, Sylvain Lemieux wrote:
> > From: Sylvain Lemieux <[email-masked]>
> > 
> > Probably most of NXP LPC32xx boards have 13MHz main oscillator
> > and therefore for HCLK PLL and ARM core clock rate default
> > hardware setting of 16 * 13MHz = 208MHz and the AHB bus clock
> > rate of 208MHz / 2 = 104MHz.
> > 
> > The change explicitly defines the peripheral PWM1/PWM2 default
> > clock output rate of 104MHz. If needed it can be redefined
> > in a board DTS file.
> > 
> > Signed-off-by: Sylvain Lemieux <[email-masked]>
> > ---
> > Note:
> > * There is a dependency on the following patch:
> >   "ARM: dts: lpc32xx: set default parent clock for pwm1 & pwm2"
> >   http://www.spinics.net/lists/arm-kernel/msg530277.html
> > * This patch should be apply after
> >   "ARM: dts: lpc32xx: add pwm-cells to base dts file"
> >   http://www.spinics.net/lists/arm-kernel/msg534050.html
> >   - There is no dependency between the patches.
> > 
> >  arch/arm/boot/dts/lpc32xx.dtsi | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/arm/boot/dts/lpc32xx.dtsi b/arch/arm/boot/dts/lpc32xx.dtsi
> > index c031c94..d669200 100644
> > --- a/arch/arm/boot/dts/lpc32xx.dtsi
> > +++ b/arch/arm/boot/dts/lpc32xx.dtsi
> > @@ -471,6 +471,7 @@
> >  				clocks = <&clk LPC32XX_CLK_PWM1>;
> >  				assigned-clocks = <&clk LPC32XX_CLK_PWM1>;
> >  				assigned-clock-parents = <&clk LPC32XX_CLK_PERIPH>;
> > +				assigned-clock-rates = <104000000>;
> 
> PWM controller clock source can be 32KHz or CLK_PERIPH, the latter is
> equal either to SYSCLK or HCLK PLL divided by HCLKDIV_CTRL[6:2].
> 
> Do you set the divider to 1? If yes, then I would say
> 
> 1) this is very specific to your board, generally CLK_PERIPH
>    is set to be about 10-13MHz,
> 2) HCLKDIV or PERIPH clock configuration shall not be done in pwm device node.
> 
> 104MHz is too high value to be set by default for PWM clock.
> 
This is a good catch; it was an error on my side.
The purpose of the patch was to setup the output of the
PWM clock to the default CLK_PERIPH value (13325000).

This change does not modify the HCLKDIV or the PERIPH clock.

I can submit a version 2 with the proper value and update
the patch description to list the default peripheral clock
setup of 13MHz.

This change is adding a default value for the PWM clock
(setup to CLK_PERIPH) to the PWM device node, allowing the
board specific DTS to only enable the PWM to get it work.

If the PWM clock output is not setup with a default value,
only enabling the PWM in the board specific DTS file is not
enough; the PWM divider will keep the default value of zero
(i.e. PWM clock off).

> --
> With best wishes,
> Vladimir

Sylvain