linux-kernel - Re: [PATCH v5] GPIO: add support for 74x164 serial-in/parallel-out 8-bit shift register

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Message-Id: <201010201442.36402.florian@openwrt.org>
Date:	Wed, 20 Oct 2010 14:42:36 +0200
From:	Florian Fainelli <florian@...nwrt.org>
To:	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Brownell <david-b@...bell.net>, Willy Tarreau <w@....eu>,
	linux-kernel@...r.kernel.org, Samuel Ortiz <sameo@...ux.intel.com>,
	Miguel Gaio <miguel.gaio@...xo.com>,
	dbrownell@...rs.sourceforge.net, Juhos Gabor <juhosg@...nwrt.org>
Subject: Re: [PATCH v5] GPIO: add support for 74x164 serial-in/parallel-out 8-bit shift register

On Wednesday 20 October 2010 10:17:32 Miguel Ojeda wrote:
> On Wed, Oct 20, 2010 at 9:52 AM, Miguel Ojeda
> 
> <miguel.ojeda.sandonis@...il.com> wrote:
> > On Wed, Oct 20, 2010 at 1:00 AM, Andrew Morton
> > 
> > <akpm@...ux-foundation.org> wrote:
> >> On Tue, 19 Oct 2010 09:26:42 +0200
> >> 
> >> Miguel Ojeda <miguel.ojeda.sandonis@...il.com> wrote:
> >>> On Mon, Oct 18, 2010 at 9:35 PM, Florian Fainelli <florian@...nwrt.org> 
wrote:
> >>> > From: Miguel Gaio <miguel.gaio@...xo.com>
> >>> > 
> >>> > This patch adds support for generic 74x164 serial-in/parallel-out
> >>> > 8-bits shift register. This driver can be used as a GPIO output
> >>> > expander.
> >>> 
> >>> ...
> >>> 
> >>> > +struct gen_74x164_chip {
> >>> > +       struct spi_device       *spi;
> >>> > +       struct gpio_chip        gpio_chip;
> >>> > +       struct mutex            lock;
> >>> > +       u8                      port_config;
> >>> > +};
> >>> 
> >>> ...
> >>> 
> >>> > +static void gen_74x164_set_value(struct gpio_chip *gc,
> >>> > +               unsigned offset, int val)
> >>> > +{
> >>> > +       struct gen_74x164_chip *chip = gpio_to_chip(gc);
> >>> > +       bool refresh;
> >>> > +
> >>> > +       mutex_lock(&chip->lock);
> >>> > +       if (val)
> >>> > +               chip->port_config |= (1 << offset);
> >>> > +       else
> >>> > +               chip->port_config &= ~(1 << offset);
> >>> 
> >>> set_bit(), clear_bit() ?
> >> 
> >> They're only to be used on `unsigned long' types, and `port_config' is
> >> u8.
> > 
> > Right as always! Maybe BIT()? Don't we have a {SET,CLEAR}_BIT()-like
> > macros somewhere?
> > 
> > #define SET_BIT(var,nr) (var) |= BIT((nr))
> > #define CLEAR_BIT(var,nr) (var) &= ~BIT((nr))
> > #define PUT_BIT(var,nr,value) do { \
> >        if ((value)) \
> >                SET_BIT((var), (nr)); \
> >        else \
> >                CLEAR_BIT((var), (nr)); \
> > } while(0)
> > 
> > May I make a patch and try to see who could use it? I suppose a
> > Coccinelle's semantic patch would be great here.
> 
> Well, after trying a few minutes spatch for my first time it has
> already found a lot of places where the macros could be applied. I
> will prepare a patch.

Though this is certainly valid, what's the benefit in using a macro to do that 
instead of open coding the toggle of a bit in a variable?
--
Florian
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