linux-kernel - Re: [PATCH v2 2/7] pwm: sun4i: Add an optional probe for reset line

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Date:   Tue, 5 Nov 2019 08:01:28 +0100
From:   Philipp Zabel <pza@...gutronix.de>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Clément Péron <peron.clem@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Jernej Skrabec <jernej.skrabec@...l.net>
Subject: Re: [PATCH v2 2/7] pwm: sun4i: Add an optional probe for reset line

On Mon, Nov 04, 2019 at 09:11:57AM +0100, Uwe Kleine-König wrote:
> Hello,
> 
> adding Philipp Zabel (= reset controller maintainer) to Cc: and so I'm
> not stripping the uncommented parts of the patch.
> 
> On Sun, Nov 03, 2019 at 09:33:29PM +0100, Clément Péron wrote:
> > From: Jernej Skrabec <jernej.skrabec@...l.net>
> > 
> > H6 PWM core needs deasserted reset line in order to work.
> > 
> > Add an optional probe for it.
> > 
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > Signed-off-by: Clément Péron <peron.clem@...il.com>
> > ---
> >  drivers/pwm/pwm-sun4i.c | 32 ++++++++++++++++++++++++++++++--
> >  1 file changed, 30 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> > index 6f5840a1a82d..d194b8ebdb00 100644
> > --- a/drivers/pwm/pwm-sun4i.c
> > +++ b/drivers/pwm/pwm-sun4i.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/of_device.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/pwm.h>
> > +#include <linux/reset.h>
> >  #include <linux/slab.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/time.h>
> > @@ -78,6 +79,7 @@ struct sun4i_pwm_data {
> >  struct sun4i_pwm_chip {
> >  	struct pwm_chip chip;
> >  	struct clk *clk;
> > +	struct reset_control *rst;
> >  	void __iomem *base;
> >  	spinlock_t ctrl_lock;
> >  	const struct sun4i_pwm_data *data;
> > @@ -365,6 +367,20 @@ static int sun4i_pwm_probe(struct platform_device *pdev)
> >  	if (IS_ERR(pwm->clk))
> >  		return PTR_ERR(pwm->clk);
> >  
> > +	pwm->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
> > +	if (IS_ERR(pwm->rst)) {
> > +		if (PTR_ERR(pwm->rst) == -EPROBE_DEFER)
> > +			return PTR_ERR(pwm->rst);
> > +		dev_info(&pdev->dev, "no reset control found\n");
> 
> I would degrade this to a dev_dbg. Otherwise this spams the log for all
> unaffected machines.

The _optional variants return NULL if the reset is not specified in the
device tree, so this is not "no reset control found", but a real error
that should be returned.

> devm_reset_control_get_optional() is defined in a section that has a
> comment "These inline function calls will be removed once all
> consumers have been moved over to the new explicit API.", so I guess
> you want devm_reset_control_get_optional_exclusive or even
> devm_reset_control_get_optional_shared here.

Correct. If this driver deasserts in probe() and asserts the reset in
remove(), this can use the refcounting _shared variant.

> @Philipp: maybe a check in checkpatch that warns about introduction of
> such new instances would be good?!

Yes, that would be helpful.

regards
Philipp