linux-kernel - Re: [patch/rfc 1/4] GPIO implementation framework

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Date:	Wed, 14 Nov 2007 14:51:22 +0800
From:	"eric miao" <eric.y.miao@...il.com>
To:	"David Brownell" <david-b@...bell.net>
Cc:	"Linux Kernel list" <linux-kernel@...r.kernel.org>,
	"Felipe Balbi" <felipebalbi@...rs.sourceforge.net>,
	"Bill Gatliff" <bgat@...lgatliff.com>,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	"Andrew Victor" <andrew@...people.com>,
	"Tony Lindgren" <tony@...mide.com>,
	"Jean Delvare" <khali@...ux-fr.org>,
	"Kevin Hilman" <khilman@...sta.com>,
	"Paul Mundt" <lethal@...ux-sh.org>,
	"Ben Dooks" <ben@...nity.fluff.org>
Subject: Re: [patch/rfc 1/4] GPIO implementation framework

On Nov 14, 2007 12:36 PM, David Brownell <david-b@...bell.net> wrote:
> On Tuesday 13 November 2007, eric miao wrote:
> > Subject: [PATCH 5/5] move per GPIO "requested" to "struct gpio_desc"
> >
>
> >  struct gpio_desc {
> >       struct gpio_chip *chip;
> >       unsigned is_out:1;
> > +     unsigned requested:1;
> > +#ifdef CONFIG_DEBUG_FS
> > +     const char *requested_str;
> > +#endif
>
> A better name for this would be "label", matching what's
> passed from gpio_request().  Ndls abrviatns r bd.
>

Fine.

>
> Note that this means (on typical 32-bit embedded hardware)
> twelve bytes per GPIO, which if you assume 256 GPIOs means
> an extra 3 KB static memory compared to the patch I sent.
>

Note this reduces the memory in gpio_chip, so it consumes almost same
memory as the patch you sent.

>
> > @@ -43,20 +43,19 @@ static inline int gpio_is_onchip(unsigned gpio,
> > struct gpio_chip *chip)
> >  /* Warn when drivers omit gpio_request() calls -- legal but
> >   * ill-advised when setting direction, and otherwise illegal.
> >   */
> > -static void gpio_ensure_requested(struct gpio_chip *chip, unsigned offset)
> > +static void gpio_ensure_requested(unsigned gpio)
>
> Simpler to pass a gpio_desc pointer ...
>
>
> >       if (!requested)
> > -             printk(KERN_DEBUG "GPIO-%d autorequested\n",
> > -                             chip->base + offset);
> > +             pr_debug("GPIO-%d autorequested\n", gpio);
>
> Leave the printk in ... this is the sort of thing we want
> to see fixed, which becomes unlikely once you hide such
> diagnostics.  And for that matter, what would be enabling
> the "-DDEBUG" that would trigger a pr_debug() message?
>

line length issue, just ignore this if you prefer.

>
>
> ... overall the main downside of these patches seems to
> be that it consumes more static memory.
>

Not really, since it reduces the holes. That all depend on your
ARCH_NR_GPIOS.

-- 
Cheers
- eric
-
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