Messages in this thread | | | Date | Thu, 20 Jan 2011 19:08:22 +0000 | From | Russell King - ARM Linux <> | Subject | Re: Locking in the clk API |
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On Thu, Jan 20, 2011 at 05:02:55PM +0000, Ben Dooks wrote: > If you want to make it so that each low-power mode has to work > out what PLLs need to be disabled and then re-enabled makes me > want to be sick. Hiding this stuff behind specific implementations > is a recipe for disaster.
Why should systems which don't suffer from such problems be prevented from gaining power saving from turning off their clocks when devices are not being used (eg, the console serial port.)
One solution to your root PLL issue would be to have a separate set of enable/disable API calls which get called at setup/release time (or whatever you'd like to call it) which can only be called from non-atomic context. Maybe clk_prepare() and clk_unprepare(). These functions should perform whatever is necessary to ensure that the clock source is available for use atomically when clk_enable() is called.
So, in your case, clk_prepare() ensures that the root PLL is enabled, clk_unprepare() allows it to be turned off.
In the case of a console driver, clk_prepare() can be called when we know the port will be used as a console. clk_enable() is then called before writing out the string, and clk_disable() after we've completely sent the last character.
This allows the best of both worlds. We now have a clk_enable() which can be used to turn the clocks off through the clock tree up to the first non-atomic clock, and we also have a way to deal with those which need to sleep. So not only do "sleeping clock" implementations become possible but these "sleeping clock" implementations also get the opportunity to shutdown some of their clock tree with minimal latency for doing so.
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