linux-kernel - Re: [PATCH 3/3] OLPC: ALSA: fix cs5535audio's MIC GPIO to enable input

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 26 Feb 2010 23:14:35 -0800
From:	David Brownell <david-b@...bell.net>
To:	Ben Gardner <gardner.ben@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andres Salomon <dilinger@...labora.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jani Nikula <ext-jani.1.nikula@...ia.com>
Subject: Re: [PATCH 3/3] OLPC: ALSA: fix cs5535audio's MIC GPIO to enable input

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.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/