Re: [PATCH v2 3/7] pwm: sun4i: Add an optional probe for bus clock

Clément Péron
2019-11-04T18:07:16Z

Hi,

On Mon, 4 Nov 2019 at 09:24, Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> wrote:
>
> Hello,
>
> On Sun, Nov 03, 2019 at 09:33:30PM +0100, Clément Péron wrote:
> > From: Jernej Skrabec <jernej.skrabec@siol.net>
> >
> > H6 PWM core needs bus clock to be enabled in order to work.
> >
> > Add an optional probe for it and a fallback for previous
> > bindings without name on module clock.
> >
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> > Signed-off-by: Clément Péron <peron.clem@gmail.com>
> > ---
> > drivers/pwm/pwm-sun4i.c | 36 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 36 insertions(+)
> >
> > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> > index d194b8ebdb00..b5e7ac364f59 100644
> > --- a/drivers/pwm/pwm-sun4i.c
> > +++ b/drivers/pwm/pwm-sun4i.c
> > @@ -78,6 +78,7 @@ 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;
> > @@ -367,6 +368,31 @@ static int sun4i_pwm_probe(struct platform_device *pdev)
>
> Adding more context here:
>
> | pwm->clk = devm_clk_get(&pdev->dev, NULL);
> > if (IS_ERR(pwm->clk))
> > return PTR_ERR(pwm->clk);
> >
> > + /* Get all clocks and reset line */
> > + pwm->clk = devm_clk_get_optional(&pdev->dev, "mod");
> > + if (IS_ERR(pwm->clk)) {
> > + dev_err(&pdev->dev, "get clock failed %ld\n",
> > + PTR_ERR(pwm->clk));
> > + return PTR_ERR(pwm->clk);
> > + }
>
> I guess you want to drop the first assignment to pwm->clk.

devm_clk_get_optional will return NULL if there is no entry, I don't
get where I need to drop it assignment.

>
> > + /* Fallback for old dtbs with a single clock and no name */
> > + if (!pwm->clk) {
> > + pwm->clk = devm_clk_get(&pdev->dev, NULL);
> > + if (IS_ERR(pwm->clk)) {
> > + dev_err(&pdev->dev, "get clock failed %ld\n",
> > + PTR_ERR(pwm->clk));
> > + return PTR_ERR(pwm->clk);
> > + }
> > + }
>
> There is a slight change of behaviour if I'm not mistaken. If you have
> this:
>
> clocks = <&clk1>;
> clock-names = "mod";
>
> pwm {
> compatible = "allwinner,sun4i-a10-pwm"
> clocks = <&clk2>;
> }
>
> you now use clk1 instead of clk2 before.
>
> Assuming this is only a theoretical problem, at least pointing this out
> in the commit log would be good I think.

Yes it's correct and as you said the driver don't check for a correct
device tree,
that why it's now optional probe.
Let's assume that's the device-tree is correct, I will add a comment
in the commit log.

>
> > + pwm->bus_clk = devm_clk_get_optional(&pdev->dev, "bus");
> > + if (IS_ERR(pwm->bus_clk)) {
> > + dev_err(&pdev->dev, "get bus_clock failed %ld\n",
> > + PTR_ERR(pwm->bus_clk));
> > + return PTR_ERR(pwm->bus_clk);
> > + }
> > +
> > pwm->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
> > if (IS_ERR(pwm->rst)) {
> > if (PTR_ERR(pwm->rst) == -EPROBE_DEFER)
> > @@ -381,6 +407,13 @@ static int sun4i_pwm_probe(struct platform_device *pdev)
> > return ret;
> > }
> >
> > + /* Enable bus clock */
> > + ret = clk_prepare_enable(pwm->bus_clk);
> > + if (ret) {
> > + dev_err(&pdev->dev, "Cannot prepare_enable bus_clk\n");
>
> I'd do s/prepare_enable/prepare and enable/ here.
Ok

>
> > + goto err_bus;
> > + }
> > +
> > pwm->chip.dev = &pdev->dev;
> > pwm->chip.ops = &sun4i_pwm_ops;
> > pwm->chip.base = -1;
> > @@ -401,6 +434,8 @@ static int sun4i_pwm_probe(struct platform_device *pdev)
> > return 0;
> >
> > err_pwm_add:
> > + clk_disable_unprepare(pwm->bus_clk);
> > +err_bus:
> > reset_control_assert(pwm->rst);
> >
> > return ret;
>
> What is that clock used for? Is it required to access the hardware
> registers? Or is it only required while the PWM is enabled? If so you
> could enable the clock more finegrainded.

Regarding the datasheet it's required to access the hardware.
page 261 : https://linux-sunxi.org/File:Allwinner_H6_V200_User_Manual_V1.1.pdf

Regards,
Clément

>
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | http://www.pengutronix.de/ |