linux-kernel - Re: [RFC PATCH 3/5] hwmon: (ds1621) Convert to use hwmon_device_register

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Date:	Sat, 6 Jul 2013 12:48:03 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jean Delvare <khali@...ux-fr.org>, lm-sensors@...sensors.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/5] hwmon: (ds1621) Convert to use
 hwmon_device_register_groups

On Sat, Jul 06, 2013 at 12:31:42PM -0700, Greg Kroah-Hartman wrote:
> On Sat, Jul 06, 2013 at 12:18:16PM -0700, Guenter Roeck wrote:
> > On Sat, Jul 06, 2013 at 08:01:51PM +0200, Jean Delvare wrote:
> > > On Sat, 6 Jul 2013 10:57:47 -0700, Greg Kroah-Hartman wrote:
> > > > On Sat, Jul 06, 2013 at 10:24:53AM -0700, Guenter Roeck wrote:
> > > > > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > > > > ---
> > > > >  drivers/hwmon/ds1621.c |   25 +++++++++----------------
> > > > >  1 file changed, 9 insertions(+), 16 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/hwmon/ds1621.c b/drivers/hwmon/ds1621.c
> > > > > index a26ba7a..f1d0fa0 100644
> > > > > --- a/drivers/hwmon/ds1621.c
> > > > > +++ b/drivers/hwmon/ds1621.c
> > > > > @@ -358,11 +358,15 @@ static const struct attribute_group ds1621_group = {
> > > > >  	.is_visible = ds1621_attribute_visible
> > > > >  };
> > > > >  
> > > > > +static const struct attribute_group *ds1621_groups[] = {
> > > > > +	&ds1621_group,
> > > > > +	NULL
> > > > > +};
> > > > > +
> > > > >  static int ds1621_probe(struct i2c_client *client,
> > > > >  			const struct i2c_device_id *id)
> > > > >  {
> > > > >  	struct ds1621_data *data;
> > > > > -	int err;
> > > > >  
> > > > >  	data = devm_kzalloc(&client->dev, sizeof(struct ds1621_data),
> > > > >  			    GFP_KERNEL);
> > > > > @@ -377,22 +381,12 @@ static int ds1621_probe(struct i2c_client *client,
> > > > >  	/* Initialize the DS1621 chip */
> > > > >  	ds1621_init_client(client);
> > > > >  
> > > > > -	/* Register sysfs hooks */
> > > > > -	err = sysfs_create_group(&client->dev.kobj, &ds1621_group);
> > > > > -	if (err)
> > > > > -		return err;
> > > > > -
> > > > > -	data->hwmon_dev = hwmon_device_register(&client->dev);
> > > > > -	if (IS_ERR(data->hwmon_dev)) {
> > > > > -		err = PTR_ERR(data->hwmon_dev);
> > > > > -		goto exit_remove_files;
> > > > > -	}
> > > > > +	data->hwmon_dev = hwmon_device_register_groups(&client->dev, data,
> > > > > +						       ds1621_groups);
> > > > > +	if (IS_ERR(data->hwmon_dev))
> > > > > +		return PTR_ERR(data->hwmon_dev);
> > > > >  
> > > > >  	return 0;
> > > > > -
> > > > > - exit_remove_files:
> > > > > -	sysfs_remove_group(&client->dev.kobj, &ds1621_group);
> > > > > -	return err;
> > > > 
> > > > Aren't your sysfs files now being created attached to a different device
> > > > than they originally were?  Before this patch, they were being attached
> > > > to the parent device of the hwmon device being created with the call to
> > > > hwmon_device_register(), and now they are attached to the device created
> > > > with that call.
> > > > 
> > > > Is that what you really want?  Can userspace handle this movement of
> > > > files?
> > > 
> > > libsensors supports both, as well as pwmconfig/fancontrol. Some drivers
> > > are already doing that so every application dealing with hwmon devices
> > > should handle it already.
> > > 
> > Yes, and I tested it with the new nct6775 driver to make sure that it works.
> > The i2c and spi drivers need some more work, though - the name attribute is
> > now missing and will have to be created for the hwmon device itself. If you have
> > an idea how to do that without adding it in every driver, please let me know.
> 
> Why do you need a name attribute at all?  Shouldn't that just be the
> name of the device, or the parent?
> 
It is part of the hwmon ABI and, at least in almost all cases, does return
the name of the device.

It is kind of similar to the 'name' attribute in i2c and spi drivers - in fact,
the drivers just use that attribute since the hwmon attributes are currently
associated with the parent device.

> Can you make the name be part of the groups always?
> 
Yes, that would be one option. All drivers except for spi and i2c drivers
already do that.

Another option would be to create a class attribute to return the parent driver
name for spi and i2c devices and otherwise the hwmon driver name. This would
reduce the amount of code needed in the drivers. Jean, do you see a problem with
that approach (except that we would have to remove explicit name attributes from
existing drivers) ?

Thanks,
Guenter
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