linux-kernel - Re: [linux-sunxi] Re: [PATCH 4/6] pwm: sun4i: Add support for H6 PWM

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Date:   Tue, 30 Jul 2019 00:09:40 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Jernej Škrabec <jernej.skrabec@...l.net>,
        Mark Rutland <mark.rutland@....com>, linux-pwm@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Sascha Hauer <kernel@...gutronix.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [linux-sunxi] Re: [PATCH 4/6] pwm: sun4i: Add support for H6 PWM

On Tue, Jul 30, 2019 at 12:07 AM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> On Mon, Jul 29, 2019 at 05:55:52PM +0200, Jernej Škrabec wrote:
> > Hi Uwe,
> >
> > Dne ponedeljek, 29. julij 2019 ob 08:40:30 CEST je Uwe Kleine-König
> > napisal(a):
> > > On Fri, Jul 26, 2019 at 08:40:43PM +0200, Jernej Skrabec wrote:
> > > > Now that sun4i PWM driver supports deasserting reset line and enabling
> > > > bus clock, support for H6 PWM can be added.
> > > >
> > > > Note that while H6 PWM has two channels, only first one is wired to
> > > > output pin. Second channel is used as a clock source to companion AC200
> > > > chip which is bundled into same package.
> > > >
> > > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > > > ---
> > > >
> > > >  drivers/pwm/pwm-sun4i.c | 10 ++++++++++
> > > >  1 file changed, 10 insertions(+)
> > > >
> > > > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> > > > index 7d3ac3f2dc3f..9e0eca79ff88 100644
> > > > --- a/drivers/pwm/pwm-sun4i.c
> > > > +++ b/drivers/pwm/pwm-sun4i.c
> > > > @@ -331,6 +331,13 @@ static const struct sun4i_pwm_data
> > > > sun4i_pwm_single_bypass = {>
> > > >   .npwm = 1,
> > > >
> > > >  };
> > > >
> > > > +static const struct sun4i_pwm_data sun50i_pwm_dual_bypass_clk_rst = {
> > > > + .has_bus_clock = true,
> > > > + .has_prescaler_bypass = true,
> > > > + .has_reset = true,
> > > > + .npwm = 2,
> > > > +};
> > > > +
> > > >
> > > >  static const struct of_device_id sun4i_pwm_dt_ids[] = {
> > > >
> > > >   {
> > > >
> > > >           .compatible = "allwinner,sun4i-a10-pwm",
> > > >
> > > > @@ -347,6 +354,9 @@ static const struct of_device_id sun4i_pwm_dt_ids[] =
> > > > {
> > > >
> > > >   }, {
> > > >
> > > >           .compatible = "allwinner,sun8i-h3-pwm",
> > > >           .data = &sun4i_pwm_single_bypass,
> > > >
> > > > + }, {
> > > > +         .compatible = "allwinner,sun50i-h6-pwm",
> > > > +         .data = &sun50i_pwm_dual_bypass_clk_rst,
> > >
> > > If you follow my suggestion for the two previous patches, you can just
> > > use:
> > >
> > >     compatible = "allwinner,sun50i-h6-pwm", "allwinner,sun5i-a10s-pwm";
> > >
> > > and drop this patch.
> >
> > Maxime found out that it's not compatible with A10s due to difference in bypass
> > bit, but yes, I know what you mean.
> >
> > Since H6 requires reset line and bus clock to be specified, it's not compatible
> > from DT binding side. New yaml based binding must somehow know that in order
> > to be able to validate DT node, so it needs standalone compatible. However,
> > depending on conclusions of other discussions, this new compatible can be
> > associated with already available quirks structure or have it's own.
>
> I cannot follow. You should be able to specify in the binding that the
> reset line and bus clock is optional. Then allwinner,sun50i-h6-pwm
> without a reset line and bus clock also verifies, but this doesn't
> really hurt (and who knows, maybe the next allwinner chip needs exactly
> this).

It is not optional. It will not work if either the clocks or reset controls
are missing. How would these be optional anyway? Either it's connected and
thus required, or it's not and therefore should be omitted from the
description.

ChenYu