From: David Brownell <david-b@pacbell.net>
To: Ben Gardner <gardner.ben@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Andres Salomon <dilinger@collabora.co.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Jani Nikula <ext-jani.1.nikula@nokia.com>
Subject: Re: [PATCH 3/3] OLPC: ALSA: fix cs5535audio's MIC GPIO to enable input
Date: Fri, 26 Feb 2010 23:14:35 -0800 [thread overview]
Message-ID: <201002262314.35871.david-b@pacbell.net> (raw)
In-Reply-To: <45a4e62ae577ae6cabce7e243e675b5e7d994ec2.1267225701.git.gardner.ben@gmail.com>
On Friday 26 February 2010, Ben Gardner wrote:
> We need to read back the value written to the GPIO pin to control the
> MIC input enable.
There are two potential values associated with GPIO outputs:
- The value you wrote to it, which you should just remember.
This value should *NEVER* be returned through the GPIO calls.
- The value at the pin, which will *often* be the same as
what you wrote to it ... except for open drain signals
or other "multi-drive" cases. Or if you try to read the
value back before it gets latched. (It's common to have
the "latch value" step be clocked by something ... and to
have multiple clock domains, so latching might not sync
up with what your CPU is doing.)
>From other patches recently landing in my mailbox, I'm thinking
that your GPIO driver isn't behaving properly ... it should return
the second value.
> Use gpio_set_direction() to set the GPIO in bidirectional mode.
NAK. THere is no such call, and should never be one.
prev parent reply other threads:[~2010-02-27 7:14 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-26 23:26 [PATCH 0/3] gpio: add gpio_set_direction Ben Gardner
2010-02-26 23:26 ` [PATCH 1/3] gpiolib: add gpio_set_direction() Ben Gardner
2010-02-26 23:39 ` Andres Salomon
2010-02-27 5:11 ` Ben Gardner
2010-02-27 7:02 ` David Brownell
2010-02-27 10:26 ` Mark Brown
2010-02-27 16:24 ` David Brownell
2010-02-27 17:20 ` Mark Brown
2010-02-27 17:51 ` David Brownell
2010-03-01 10:35 ` Mark Brown
2010-02-27 18:36 ` Ben Gardner
2010-02-27 19:23 ` David Brownell
2010-02-27 18:36 ` [PATCH] cs5535-gpio: change input/output enable to match gpiolib expectations Ben Gardner
2010-02-27 18:40 ` Ben Gardner
2010-02-27 18:56 ` [PATCH v2] " Ben Gardner
2010-02-27 19:18 ` David Brownell
2010-02-26 23:26 ` [PATCH 2/3] cs5535-gpio: Use set_direction Ben Gardner
2010-02-27 7:04 ` David Brownell
2010-02-27 18:18 ` Ben Gardner
2010-02-26 23:26 ` [PATCH 3/3] OLPC: ALSA: fix cs5535audio's MIC GPIO to enable input Ben Gardner
2010-02-27 7:14 ` David Brownell [this message]
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