From: Jeff Garzik <jgarzik@pobox.com>
To: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [BUG] unsafe reset in ac97_codec.c
Date: Wed, 04 Feb 2004 16:24:22 -0500 [thread overview]
Message-ID: <40216306.2010602@pobox.com> (raw)
In-Reply-To: <1075822947.5204.506.camel@cearnarfon>
Liam Girdwood wrote:
> /* probing AC97 codec, AC97 2.0 says that bit 15 of register 0x00
> (reset) should
> * be read zero.
> *
> * FIXME: is the following comment outdated? -jgarzik
> * Probing of AC97 in this way is not reliable, it is not even SAFE !!
> */
> codec->codec_write(codec, AC97_RESET, 0L);
>
>
> IMO, this is unsafe because it can also reset the codec into it's
> default power state which can be "power down". This is not normally a
> problem for PC's, but some battery powered devices have the default
> codec state as "power down" to conserve power.
>
> Was this introduced as a workaround for some buggy device ?
> If no one objects I'll submit a patch.
In general it's important for Linux to be able to reset a device
reliable. Where in Other Operating Systems one must reboot the
computer, Linux users can just re-load the driver quite often.
So I think there are two comments here:
* I can certainly see -probing- being unreliable (but not necessarily reset)
* If the default state for some devices is power-down, the driver should
be aware of that -anyway-, and we should power up on startup or on-demand.
Jeff
next prev parent reply other threads:[~2004-02-04 21:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-03 15:42 [BUG] unsafe reset in ac97_codec.c Liam Girdwood
2004-02-04 21:24 ` Jeff Garzik [this message]
2004-02-05 16:31 ` Liam Girdwood
2004-02-05 17:59 ` Alan Cox
2004-02-26 15:55 ` Liam Girdwood
2004-02-29 18:38 ` Jeff Garzik
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