Re: [PATCH] arm: dts: fix rk3066a based boards vdd_log voltage initialization

Heiko Stuebner
2016-09-19T16:15:23Z

Am Montag, 19. September 2016, 08:15:30 CEST schrieb Doug Anderson:
> Hi,
>
> On Mon, Sep 19, 2016 at 1:44 AM, Andy Yan <andy.yan@rock-chips.com> wrote:
> > The current rk3066a based boards(Rayeager, Bqcurie2, Marsboard) use
> > pwm modulate vdd_logic voltage, but the pwm is default disabled and
> > the pwm pin acts as a gpio before pwm regulator probed, so the pwm
> > regulator driver will get a zero dutycycle at probe time, so change
> > the initial dutycycle to zero to match pwm_regulator_init_state check.
> >
> > Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
> >
> > ---
> >
> > arch/arm/boot/dts/rk3066a-bqcurie2.dts | 2 +-
> > arch/arm/boot/dts/rk3066a-marsboard.dts | 2 +-
> > arch/arm/boot/dts/rk3066a-rayeager.dts | 2 +-
> > 3 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm/boot/dts/rk3066a-bqcurie2.dts
> > b/arch/arm/boot/dts/rk3066a-bqcurie2.dts index bc674ee..618450d 100644
> > --- a/arch/arm/boot/dts/rk3066a-bqcurie2.dts
> > +++ b/arch/arm/boot/dts/rk3066a-bqcurie2.dts
> > @@ -61,7 +61,7 @@
> >
> > regulator-min-microvolt = <1200000>;
> > regulator-max-microvolt = <1200000>;
> > regulator-always-on;
> >
> > - voltage-table = <1000000 100>,
> > + voltage-table = <1000000 0>,
>
> In my opinion this isn't quite the right answer. I think that you
> should add a new property describing the voltage in the case that the
> pin is an input and you should fill that property in, like:
>
> voltage-when-input = <1000000>;

I'd think this would be more of a pwm issue, not something the pwm-regulator
should need to care about.

Ideally the pwm driver should be able to return some state information even if
disabled? I.e. deriving a duty-cycle value from its pin state similar to what
Doug described below (it's either 0% or 100%)

But right now I have a hard time understanding how the pwm could return any
duty-cycle information for an input gpio to the pwm-regulator, as I assume the
pwm-driver has to probe (and thus set pinctrl to the pwm function) before the
pwm-regulator is able to get the pwm handle?

> Once you have this property you should ideally be able to read whether
> the pin is currently configured as an input or as a special function
> at bootup. Note that I don't actually know if this is possible with
> the current pinctrl API, but it does seem like the ideal way to do it
> since it means you'll work even if the BIOS changes (AKA: if the BIOS
> leaves the pin as an input you can keep the voltage the same and if
> the BIOS leaves the pin as PWM you can keep the voltage the same).
>
> It's also possible that you could just add a property that says "init
> to a certain value at bootup no matter what the BIOS left it as". As
> long as that voltage is the maximum (and you'll lower it later) this
> ought to be safe and you shouldn't risk temporarily undervolting
> things.
>
>
> Note that, if you haven't already done so, you almost certainly want
> to make sure your pinctrl species an "init" state in addition to a
> "default" state. See <https://patchwork.kernel.org/patch/7454311/>.
>
> -Doug