Re: [BUG] unsafe reset in ac97_codec.c

[Jeff Garzik <jgarzik@pobox.com>]

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 * FIXME: is the following comment outdated?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