linux-kernel - Re: PATCH [1/3] drivers/input/xpad.c: Improve Xbox 360 wireless support and add sysfs interface

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Message-ID: <20090302215910.GA31164@kroah.com>
Date:	Mon, 2 Mar 2009 13:59:10 -0800
From:	Greg KH <greg@...ah.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	mamurph@...clemson.edu, linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org, linux-usb@...r.kernel.org,
	oliver@...kum.org, fweisbec@...il.com,
	torvalds@...ux-foundation.org
Subject: Re: PATCH [1/3] drivers/input/xpad.c: Improve Xbox 360 wireless
	support  and add sysfs interface

On Mon, Mar 02, 2009 at 01:35:51PM -0800, Andrew Morton wrote:
> On Mon, 2 Mar 2009 13:18:20 -0800
> Greg KH <greg@...ah.com> wrote:
> 
> > On Mon, Mar 02, 2009 at 01:04:25PM -0800, Andrew Morton wrote:
> > > On Sat, 28 Feb 2009 23:53:03 -0500
> > > Mike Murphy <mamurph@...clemson.edu> wrote:
> > > > ...
> > > >
> > > > +static ssize_t xpad_show_int(struct device *dev, struct device_attribute *attr,
> > > > +		char *buf)
> > > > +{
> > > > +	struct usb_xpad *xpad = to_xpad(dev);
> > > > +	int value;
> > > > +	if (attr == &dev_attr_rumble_enable)
> > > > +		value = xpad->rumble_enable;
> > > > +	else if (attr == &dev_attr_controller_number)
> > > > +		value = xpad->controller_number;
> > > > +	else if (attr == &dev_attr_controller_present)
> > > > +		value = xpad->controller_present;
> > > > +	else if (attr == &dev_attr_controller_type)
> > > > +		value = xpad->controller_type;
> > > > +	else if (attr == &dev_attr_left_trigger_full_axis)
> > > > +		value = xpad->left_trigger_full_axis;
> > > > +	else if (attr == &dev_attr_right_trigger_full_axis)
> > > > +		value = xpad->right_trigger_full_axis;
> > > > +	else
> > > > +		return -EIO;
> > > > +	return snprintf(buf, PAGE_SIZE, "%d\n", value);
> > > > +}
> > > 
> > > The code's a bit unusual.  Most drivers don't have all that
> > > if-then-else stuff.  They use a separate function for each sysfs file
> > > and then they wrap it all up into a macro which emits all the data and
> > > code for each file.
> > 
> > Yes, most don't, but that is because we used to not pass the attribute
> > variable to the show/store functions.  It was added so that we could
> > reduce the huge numbers of functions needed, to do stuff like this.  The
> > hwmon drivers are examples of other drivers that do their show/store
> > like this.
> > 
> > There's nothing wrong with it that I can see.
> > 
> 
> OK.  I think.
> 
> - This approach will require a large number of edits each time an
>   attribute is added/removed.

That's really not a big dea.

> - otoh, removing nasty macros is always nice.
> 
> - This approach will generate slower code (which doesn't matter
>   here).

True.

> - Was it demonstrated that this approach generates less code?

Yes it was.  I can go dig through the archives if you want real numbers.

thanks,

greg k-h
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