linux-kernel - Re: [PATCH v2 3/3] hwmon: (lm75) Add regulator support

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Date:   Tue, 29 Sep 2020 14:05:12 +0000
From:   "Bedel, Alban" <alban.bedel@...q.com>
To:     "linux@...ck-us.net" <linux@...ck-us.net>
CC:     "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH v2 3/3] hwmon: (lm75) Add regulator support

On Mon, 2020-09-28 at 09:39 -0700, Guenter Roeck wrote:
> On Mon, Sep 28, 2020 at 05:39:23PM +0200, Alban Bedel wrote:
> > Add regulator support for boards where the sensor first need to be
> > powered up before it can be used.
> > 
> > Signed-off-by: Alban Bedel <alban.bedel@...q.com>
> > ---
> > v2: Rely on dummy regulators instead of explicitly handling missing
> >     regulator
> > ---
> >  drivers/hwmon/lm75.c | 23 +++++++++++++++++++++--
> >  1 file changed, 21 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
> > index ba0be48aeadd..e394df648c26 100644
> > --- a/drivers/hwmon/lm75.c
> > +++ b/drivers/hwmon/lm75.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/of.h>
> >  #include <linux/regmap.h>
> >  #include <linux/util_macros.h>
> > +#include <linux/regulator/consumer.h>
> >  #include "lm75.h"
> >  
> >  /*
> > @@ -101,6 +102,7 @@ static const unsigned short normal_i2c[] = {
> > 0x48, 0x49, 0x4a, 0x4b, 0x4c,
> >  struct lm75_data {
> >  	struct i2c_client		*client;
> >  	struct regmap			*regmap;
> > +	struct regulator		*vs;
> >  	u8				orig_conf;
> >  	u8				current_conf;
> >  	u8				resolution;	/* In bits, 9 to 16
> > */
> > @@ -540,6 +542,7 @@ static void lm75_remove(void *data)
> >  	struct i2c_client *client = lm75->client;
> >  
> >  	i2c_smbus_write_byte_data(client, LM75_REG_CONF, lm75-
> > >orig_conf);
> > +	regulator_disable(lm75->vs);
> >  }
> >  
> >  static int
> > @@ -567,6 +570,10 @@ lm75_probe(struct i2c_client *client, const
> > struct i2c_device_id *id)
> >  	data->client = client;
> >  	data->kind = kind;
> >  
> > +	data->vs = devm_regulator_get(dev, "vs");
> > +	if (IS_ERR(data->vs))
> > +		return PTR_ERR(data->vs);
> > +
> >  	data->regmap = devm_regmap_init_i2c(client,
> > &lm75_regmap_config);
> >  	if (IS_ERR(data->regmap))
> >  		return PTR_ERR(data->regmap);
> > @@ -581,11 +588,19 @@ lm75_probe(struct i2c_client *client, const
> > struct i2c_device_id *id)
> >  	data->sample_time = data->params->default_sample_time;
> >  	data->resolution = data->params->default_resolution;
> >  
> > +	/* Enable the power */
> > +	err = regulator_enable(data->vs);
> > +	if (err) {
> > +		dev_err(dev, "failed to enable regulator: %d\n", err);
> > +		return err;
> > +	}
> > +
> >  	/* Cache original configuration */
> >  	status = i2c_smbus_read_byte_data(client, LM75_REG_CONF);
> >  	if (status < 0) {
> >  		dev_dbg(dev, "Can't read config? %d\n", status);
> > -		return status;
> > +		err = status;
> > +		goto disable_regulator;
> 
> The point of using devm_add_action_or_reset() was specifically to avoid having
> to have the cleanup gotos. On top of that, the lm75_remove() function was
> specifically intended to clean up configuration data, not to do anything else.
> While hijacking lm75_remove() to also disable the regulator is technically
> correct, it makes the code more difficult to understand, and it creates a
> potential source for subsequently introduced bugs. Right now I am not inclined
> to accept this code as-is. Please provide arguments for handling the cleanup
> this way instead of using devm_add_action_or_reset().

I wrote it that way to keep the memory usage lower, but I see your
point and will update the patch accordingly.

Alban


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