From: David Brownell <david-b@pacbell.net>
To: Trent Piepho <tpiepho@freescale.com>
Cc: Jean Delvare <khali@linux-fr.org>,
Linux Kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [patch/rfc 2/4] pcf875x I2C GPIO expander driver
Date: Fri, 4 Apr 2008 19:51:24 -0700 [thread overview]
Message-ID: <200804041951.24653.david-b@pacbell.net> (raw)
In-Reply-To: <Pine.LNX.4.64.0804041102230.20532@t2.domain.actdsltmp>
On Friday 04 April 2008, Trent Piepho wrote:
> >> + if (test_bit(FLAG_IS_OUT, &gdesc->flags)) {
> >> + return -EINVAL;
> >> + /* strcpy(buf, "-1\n"); return 4; */ /* Or this? */
> >
> > Why not just return gpio_get_value(n) in all cases?
That's the right answer...
> > User might want to
> > know which value is currently being output.
>
> I thought the gpiolib layer didn't let you read an output, but I see that's
> not the case now. Maybe it's changed since the first revision? I've changed
> this to call gpio_get_value(n) for outputs too.
I don't recall ever disallowing reading output values ... the
exact behavior is platform-specific, though it "should" be the
value actually sensed at the pin, which might not be the same
as what's being driven.
> Though for the MPC8572 GPIO driver I wrote, it doesn't support reading
> outputs. The hardware doesn't allow it (IMHO, a design flaw), and working
> around this significantly slows down GPIO functions.
Then don't worry about it. Any portable code can't rely on
being able to do that.
- Dave
> What I'm trying to do
> with the GPIO lines is going to be slower than desired no matter how fast I
> make the gpio code (which is almost entirely responsible for the final speed),
> so slowing down reads by a factor of four or more just to read back outputs
> isn't desirable.
>
next prev parent reply other threads:[~2008-04-05 3:21 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=200804041951.24653.david-b@pacbell.net \
--to=david-b@pacbell.net \
--cc=khali@linux-fr.org \
--cc=linux-kernel@vger.kernel.org \
--cc=tpiepho@freescale.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).