Messages in this thread | | | Date | Fri, 21 Jan 2011 22:02:38 +0000 | From | Russell King - ARM Linux <> | Subject | Re: Locking in the clk API |
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On Fri, Jan 21, 2011 at 04:53:44PM -0500, Nicolas Pitre wrote: > So I think that the API must be augmented with more methods, such as: > > clk_slow_enable(): > - may sleep > - may be a no-op if the clk_fast_enable() is supported > > clk_fast_enable(): > - may not sleep, used in atomic context > - may be a no-op if controlling the clock takes time, in which case > clk_slow_enable() must have set the clock up entirely > > ... and similar for clk_slow_disable() and clk_fast_disable().
Isn't this along the same lines as my clk_prepare() vs clk_enable() suggestion?
I suggested that clk_prepare() be callable only from non-atomic contexts, and do whatever's required to ensure that the clock is available. That may end up enabling the clock as a result.
clk_enable() callable from atomic contexts, and turns the clock on if the hardware supports such an operation.
So, if you have something like:
Xtal--->PLL--->Routing/Masking--->Device
clk = clk_get() returns the clock for the device.
clk_prepare(clk) would walk up the clock tree, selecting the routing and preparing each clock. Clocks prior to _and_ including the PLL would need to be enabled.
clk_enable(clk) would walk up the tree if the clock isn't already enabled, calling clk_enable() on the parent clock. As we require prepared clocks to already be enabled, this automatically stops at the PLL.
To encourage correct usage, we just need to make sure that clk_prepare() has a might_sleep() thing, and clk_enable() throws a fit if it's used on a clk without prepare being used first. The second point is not easy to do in a foolproof manner though, but doing _something_ is better than nothing.
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