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

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Date:	Mon, 2 Mar 2009 13:35:51 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Greg KH <greg@...ah.com>
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, 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.

- otoh, removing nasty macros is always nice.

- This approach will generate slower code (which doesn't matter
  here).

- Was it demonstrated that this approach generates less code?


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