linux-kernel - Re: [PATCH RFC] pwm: add sysfs interface

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Message-Id: <201303051546.13636.poeschel@lemonage.de>
Date:	Tue, 5 Mar 2013 15:46:13 +0100
From:	Lars Poeschel <poeschel@...onage.de>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Lars Poeschel <larsi@....tu-dresden.de>,
	thierry.reding@...onic-design.de, rob@...dley.net,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH RFC] pwm: add sysfs interface

At first: Thanks for your review!

On Monday 25 February 2013 at 05:00:25, Greg KH wrote:
> On Tue, Feb 19, 2013 at 03:27:41PM +0100, Lars Poeschel wrote:
> > +static int pwmchip_export(struct pwm_chip *chip)
> > +{
> > +	int status;
> > +	struct device *dev;
> > +
> > +	mutex_lock(&sysfs_lock);
> > +	dev = device_create(&pwm_class, chip->dev, MKDEV(0, 0), chip,
> > +				"pwmchip%d", chip->base);
> > +	if (!IS_ERR(dev))
> > +		status = sysfs_create_group(&dev->kobj, &pwmchip_attr_group);
> > +	else
> > +		status = PTR_ERR(dev);
> 
> You can't create sysfs files after the device has been exposed to
> userspace.  Please use the default group functionality for the class,
> which fixes this problem.

I don't understand, what is wrong here. This is the same that gpio sysfs 
does. Could you please be a bit more specific ?
I create a new device using device_create and create a new group with it with 
some attributes. Isn't it exposed to userspace after that ?
Or am I not allowed to use pwm_class on device creation ? What to use then ?
What do you mean by default group functionality for the class ? I want to use 
my own "pwm" class ? Don't I ?

Regards,
Lars
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