From: "eric miao" <eric.y.miao@gmail.com>
To: "David Brownell" <david-b@pacbell.net>
Cc: "Linux Kernel list" <linux-kernel@vger.kernel.org>,
"Felipe Balbi" <felipebalbi@users.sourceforge.net>,
"Bill Gatliff" <bgat@billgatliff.com>,
"Haavard Skinnemoen" <hskinnemoen@atmel.com>,
"Andrew Victor" <andrew@sanpeople.com>,
"Tony Lindgren" <tony@atomide.com>,
"Jean Delvare" <khali@linux-fr.org>,
"Kevin Hilman" <khilman@mvista.com>,
"Paul Mundt" <lethal@linux-sh.org>,
"Ben Dooks" <ben@trinity.fluff.org>
Subject: Re: [patch/rfc 1/4] GPIO implementation framework
Date: Wed, 14 Nov 2007 15:36:39 +0800 [thread overview]
Message-ID: <f17812d70711132336x11190c67xd8cf20efbe914809@mail.gmail.com> (raw)
In-Reply-To: <200711132319.48821.david-b@pacbell.net>
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@pacbell.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
next prev parent reply other threads:[~2007-11-14 7:36 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <200710291809.29936.david-b@pacbell.net>
2007-10-30 1:51 ` [patch/rfc 1/4] GPIO implementation framework David Brownell
2007-11-05 21:05 ` David Brownell
2007-11-13 2:28 ` eric miao
2007-11-13 19:06 ` David Brownell
2007-11-14 0:57 ` eric miao
2007-11-14 1:00 ` eric miao
2007-11-14 1:02 ` eric miao
2007-11-14 1:03 ` eric miao
2007-11-14 1:04 ` eric miao
2007-11-14 1:04 ` eric miao
2007-11-14 4:36 ` David Brownell
2007-11-14 6:51 ` eric miao
2007-11-14 7:19 ` David Brownell
2007-11-14 7:36 ` eric miao [this message]
2007-11-17 10:38 ` Jean Delvare
2007-11-17 17:36 ` David Brownell
2007-11-20 15:20 ` Jean Delvare
2007-11-14 4:18 ` David Brownell
2007-11-14 6:46 ` eric miao
2007-11-14 3:28 ` David Brownell
2007-11-14 3:25 ` David Brownell
2007-11-14 3:53 ` David Brownell
2007-11-14 6:37 ` eric miao
2007-11-14 3:30 ` David Brownell
2007-11-14 6:40 ` eric miao
2007-11-14 7:08 ` David Brownell
2007-11-27 1:46 ` David Brownell
2007-11-27 10:58 ` eric miao
2007-11-27 17:26 ` David Brownell
2007-11-27 19:03 ` David Brownell
2007-11-27 19:29 ` David Brownell
2007-11-28 5:11 ` eric miao
2007-11-28 3:15 ` [patch/rfc 2.6.24-rc3-mm] gpiolib grows a gpio_desc David Brownell
2007-11-28 9:10 ` eric miao
2007-11-28 9:53 ` David Brownell
2007-10-30 1:51 ` [patch/rfc 2/4] pcf875x I2C GPIO expander driver David Brownell
2007-11-30 12:32 ` Jean Delvare
2007-11-30 13:04 ` Bill Gatliff
2007-11-30 13:36 ` Jean Delvare
2007-11-30 14:09 ` Bill Gatliff
2007-11-30 18:40 ` David Brownell
2007-11-30 20:13 ` Jean Delvare
2007-11-30 20:59 ` David Brownell
2008-04-04 2:06 ` Trent Piepho
2008-04-04 2:45 ` Ben Nizette
2008-04-04 3:33 ` Trent Piepho
2008-04-04 4:57 ` Ben Nizette
2008-04-05 4:05 ` userspace GPIO access (WAS: [patch/rfc 2/4] pcf875x ...) David Brownell
2008-04-07 17:56 ` Trent Piepho
2008-04-04 8:09 ` [patch/rfc 2/4] pcf875x I2C GPIO expander driver Jean Delvare
2008-04-04 19:07 ` Trent Piepho
2008-04-04 19:36 ` Jean Delvare
2008-04-04 20:18 ` Trent Piepho
2008-04-05 2:51 ` David Brownell
2008-04-05 2:53 ` David Brownell
2007-12-06 3:03 ` [patch/rfc 2/4] pcf857x " David Brownell
2007-12-06 23:17 ` Jean Delvare
2007-12-07 4:02 ` David Brownell
2007-10-30 1:53 ` [patch/rfc 3/4] DaVinci platform uses new GPIOLIB David Brownell
2007-10-30 1:54 ` [patch/rfc 4/4] DaVinci EVM uses pcf857x GPIO driver David Brownell
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