Re: [PATCH 3/6] pwm: sun4i: Add a quirk for bus clock

Uwe Kleine-König
2019-07-29T16:14:42Z

Hello Jernej,

On Mon, Jul 29, 2019 at 05:48:36PM +0200, Jernej Škrabec wrote:
> Dne ponedeljek, 29. julij 2019 ob 08:38:25 CEST je Uwe Kleine-König
> napisal(a):
> > Hello,
> >
> > On Fri, Jul 26, 2019 at 08:40:42PM +0200, Jernej Skrabec wrote:
> > > H6 PWM core needs bus clock to be enabled in order to work.
> > >
> > > Add a quirk for it.
> > >
> > > Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> > > ---
> > >
> > > drivers/pwm/pwm-sun4i.c | 15 +++++++++++++++
> > > 1 file changed, 15 insertions(+)
> > >
> > > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> > > index 1b7be8fbde86..7d3ac3f2dc3f 100644
> > > --- a/drivers/pwm/pwm-sun4i.c
> > > +++ b/drivers/pwm/pwm-sun4i.c
> > > @@ -72,6 +72,7 @@ static const u32 prescaler_table[] = {
> > >
> > > };
> > >
> > > struct sun4i_pwm_data {
> > >
> > > + bool has_bus_clock;
> > >
> > > bool has_prescaler_bypass;
> > > bool has_reset;
> > > unsigned int npwm;
> > >
> > > @@ -79,6 +80,7 @@ struct sun4i_pwm_data {
> > >
> > > struct sun4i_pwm_chip {
> > >
> > > struct pwm_chip chip;
> > >
> > > + struct clk *bus_clk;
> > >
> > > struct clk *clk;
> > > struct reset_control *rst;
> > > void __iomem *base;
> > >
> > > @@ -382,6 +384,16 @@ static int sun4i_pwm_probe(struct platform_device
> > > *pdev)>
> > > reset_control_deassert(pwm->rst);
> > >
> > > }
> > >
> > > + if (pwm->data->has_bus_clock) {
> > > + pwm->bus_clk = devm_clk_get(&pdev->dev, "bus");
> >
> > Similar to my suggestion in patch 2: I'd use devm_clk_get_optional() and
> > drop struct sun4i_pwm_data::has_bus_clock.
>
> This one is not so simple. This patch has incorrect logic. Correct logic would
> be to use "devm_clk_get(&pdev->dev, NULL)" for variants without bus clock as
> it is done already and "devm_clk_get(&pdev->dev, "bus")" and
> "devm_clk_get(&pdev->dev, "mod")" for variants with bus clock.

Then maybe something like the following?:

busclk = devm_clk_get_optional(..., "bus");
modclk = devm_clk_get_optional(..., "mod");

/*
* old dtbs might have a single clock but no clock names. Fall
* back to this for compatibility reasons.
*/
if (!modclk) {
modclk = devm_clk_get(..., NULL);
}

> You see, DT nodes for other variants don't have clock-names property at all.
> If it would be specified, it would be "mod". So, DT nodes for other variants
> have "mod" clock specified on first place (the only one), while H6 DT node will
> have "mod" clock specified on second place (see one of e-mails from Maxime), so
> "NULL" can't be used instead of "mod" in both cases.
>
> So I would say quirk is beneficial to know if you have to look up clocks by
> name or you just take first clock specified.

Best regards
Uwe

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