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

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Message-ID: <f17812d70711132336x11190c67xd8cf20efbe914809@mail.gmail.com>
Date:	Wed, 14 Nov 2007 15:36:39 +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

Y, the IRQ <--> GPIO mapping is another thing I'm concerned about. Other than
that, all the other part of the gpiolib is a great work, actually,
I've been waiting
for this for quite a long time and just don't have time for a hands-on until
recently.

So let's get more feedback on this.

On Nov 14, 2007 3:19 PM, David Brownell <david-b@...bell.net> wrote:
>
> > > >  struct gpio_desc {
> > > >       struct gpio_chip *chip;
> > > >       unsigned is_out:1;
> > > > +     unsigned requested:1;
> > > > +#ifdef CONFIG_DEBUG_FS
> > > > +     const char *requested_str;
> > > > +#endif
> > >
> > > 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.
>
> Actually, 2K is a more accurate number -- ignore DEBUG_FS.
>
>
> > Note this reduces the memory in gpio_chip, so it consumes almost same
> > memory as the patch you sent.
>
> No; the amount of space shaved from a typical (32-bit banks)
> gpio_chip is *exactly* the cost of one gpio_desc:  two words.
> In one case, two bitmaps.  In the other, a pointer, two bits,
> and internal struct padding.
>
> So unless each bank has only a single GPIO, this approach
> does cost more memory.  Both for the extra memory associated
> with each gpio_chip that's used, and for unused gpio_desc.
>
> That's not necessarily a bad thing, though it's always worth
> avoiding bloat.
>

Well, absolutely agree on this.

> - Dave
>



-- 
Cheers
- eric
-
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