linux-kernel - Re: [PATCH v3 1/6] Documentation: ARM: sunxi: pwm: add Allwinner sun8i.

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Date:   Mon, 3 Dec 2018 10:28:09 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Hao Zhang <hao5781286@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>, wens@...e.org,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>, thierry.reding@...il.com,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v3 1/6] Documentation: ARM: sunxi: pwm: add Allwinner
 sun8i.

Hi!

(Please keep all the recipiens in Cc)

On Sun, Dec 02, 2018 at 12:13:21AM +0800, Hao Zhang wrote:
> Maxime Ripard <maxime.ripard@...tlin.com> 于2018年11月27日周二 下午6:33写道：
> >
> > On Tue, Nov 27, 2018 at 09:35:23AM +0100, Uwe Kleine-König wrote:
> > > Hello,
> > >
> > > On Tue, Nov 27, 2018 at 08:52:26AM +0100, Maxime Ripard wrote:
> > > > On Mon, Nov 26, 2018 at 12:18:59AM +0800, Hao Zhang wrote:
> > > > > +  - clocks: From common clock binding, handle to the parent clock.
> > > > > +  - clock-names: Must contain the clock names described just above.
> > > >
> > > > [...]
> > > >
> > > > You seem to have used mux-0 and mux-1 for the clock names. I guess we
> > > > don't have to use a name there, we can simply use the position to find
> > > > out (as long as it's documented in the binding)
> > >
> > > I also wondered if the driver relies on the fact that the second clock
> > > is the faster running one. Is this sensible?
> >
> > Not really, I'm not sure we can make those expectations in the DT
> > binding, especially since clock rate can change at runtime.
>
> How about just add one clock on DT, most of the time, 24MHZ is enough
> (apb1 is 100MHZ)
> other one just use as a optional.
> clock rate change at runtime would make the same pair pwm channel
> uncontrollable,
> because previous one would be change by the new one different setting.

The DT is a hardware representation. If the hardware block can use
both clocks, it should be described.

Now, you can totally use only one clock of these 2 in your driver if that's
easier / more reasonable.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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