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

From: Philipp Zabel <pza@pengutronix.de>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	linux-pwm@vger.kernel.org,
	"Jernej Skrabec" <jernej.skrabec@siol.net>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Maxime Ripard" <mripard@kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Chen-Yu Tsai" <wens@csie.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Clément Péron" <peron.clem@gmail.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/7] pwm: sun4i: Add an optional probe for reset line
Date: Tue, 5 Nov 2019 08:01:28 +0100	[thread overview]
Message-ID: <20191105070128.ve73ha5ibiymcxnx@pengutronix.de> (raw)
In-Reply-To: <20191104081157.373v22atswsaktbe@pengutronix.de>

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@siol.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@siol.net>
> > Signed-off-by: Clément Péron <peron.clem@gmail.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

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