Re: [RFC] dynamic device power management proposal

[Pavel Machek <pavel@ucw.cz>]

Hi!

> | > And latency may be ignorable in a laptop environment, but it absolutely
> | > isn't in embedded devices, which users expect to operate immediately, as
> | > though they were gear-driven rather than computer-driven.
> | 
> | What latency are you talking about? Powering up piece of hw takes one
> | milisecond or something. If your /dev/dsp takes 3 seconds to power up,
> | you probably need userspace policy daemon. But that is not the case,
> | hw takes few miliseconds to wake up.
> 
> Sure, but *some* devices take substantially longer to power up or
> down.  If you insist that the driver should make the power down
> decision, then you lump high-latency and low-latency devices together,
> even though high-latency devices might be better served by separating
> the semantics.

High-latency devices indeed may be served better by separating the
semantics. Fortunately the high-latency (we are talking >50msec here,
right?) are rare enough... Like "none" in most embedded
systems... Actually only common high-latency device is harddrive
(spinup/spindown), and that's already handled specially with userspace
hooks.

									Pavel

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