Re: [PATCH v3] Add bt8xxgpio driver

From: Domenico Andreoli <cavokz@gmail.com>
To: Michael Buesch <mb@bu3sch.de>
Cc: David Brownell <david-b@pacbell.net>,
	video4linux-list@redhat.com,
	Mauro Carvalho Chehab <mchehab@infradead.org>
Subject: Re: [PATCH v3] Add bt8xxgpio driver
Date: Mon, 14 Jul 2008 17:25:50 +0200	[thread overview]
Message-ID: <20080714152550.GA32470@ska.dandreoli.com> (raw)
In-Reply-To: <200807141558.29582.mb@bu3sch.de>

On Mon, Jul 14, 2008 at 03:58:29PM +0200, Michael Buesch wrote:
> On Monday 14 July 2008 09:27:33 Domenico Andreoli wrote:
> > +static u32 nr_to_mask(struct bttv_gpiolib_device *dev, unsigned nr)
> > +{
> > +	u32 io_mask = dev->in_mask | dev->out_mask;
> > +	int shift = 0;
> > +
> > +	while(io_mask && nr) {
> > +		nr -= io_mask & 1;
> > +		io_mask >>= 1;
> > +		shift++;
> > +	}
> > +
> > +	return 1 << shift;
> > +}
> 
> This loop is really really weird.
> What the hell are you doing here?
> You ususally convert GPIO numbers to masks by doing (1 << nr), only.

gpiolib does not allow holes in the number space of gpios. once you
set chip.ngpio, you get a contiguous slice.

should the board have some of its gpio connected to something private,
they are not to be exported to gpiolib and to the user.

indeed once, as a user, I know to have a board which has n inputs and
m output and z in/out, that's all, I do not want to know how many GPIOs
actually are on the board and how are connected.

nr_to_mask() hides those holes to the user, it maps a pin iff it is
available for gpiolib fiddling.

thanks,
Domenico

-----[ Domenico Andreoli, aka cavok
 --[ http://www.dandreoli.com/gpgkey.asc
   ---[ 3A0F 2F80 F79C 678A 8936  4FEE 0677 9033 A20E BC50

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