On Wednesday 21 March 2007 2:39 pm, Pavel Machek wrote:
> > > USB gets the dependencies right, just copy that.
> > Does USB include all kinds of dependence, eg non parent-children
> > dependence?
>
> No, probably not, as USB was designed properly.
It was designed to work with as few wires as possible: "minimalist"
design. That's not the same as "proper"; not everything works with
the same design constraints.
> How common are those cross dependencies?
Common. SOC audio setups are relatively simple examples, which
I know have been making trouble on Linux for some time. One hopes
that the new ALSA SOC stuff helps sort this out:
- SOC serial controller (I2S, AC97, McBSP, SII, etc) manages
encoded data bitsteams (e.g. N channels, PCM or uLaw, etc)
for input, output, or both.
- External codec interprets those bitstreams.
- That codec is controlled using I2C, SPI, or some other bus
for control, e.g. "set volume", "enter stereo mode".
- The codec and serial controllers have separate power controls.
Think of this as separate control, data, and power channels;
which are not multiplexed like USB.
At the hardware level it probably looks like two different driver
model devices (I2S/etc, and codec) that could have semi-generic
drivers (I think this is what the ALSA SOC stuff is aiming for),
plus board-specific "power codec on/off" interfaces. Then there
are the /dev interfaces ALSA creates for each functionality.
> Do we really want to solve them generically?
What we need to be generic is: PM not preventing good solutions.
I'm not sure we're there yet.
- Dave
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