On Tue, Aug 11, 2015 at 10:23:46PM +0300, Grygorii Strashko wrote: > Hi All, > > On 08/04/2015 06:36 PM, Russell King - ARM Linux wrote: > > On Tue, Aug 04, 2015 at 10:23:31AM -0500, Nishanth Menon wrote: > >> Consider clk_enable/disable/set_parent/setfreq operations. none of these > >> operations are "atomic" from hardware point of view. instead, they are a > >> set of steps which culminates to moving from state A to state B of the > >> clock tree configuration. > > > > There's a world of difference between clk_enable()/clk_disable() and > > the rest of the clk API. > > > > clk_enable()/clk_disable() _should_ be callable from any context, since > > you may need to enable or disable a clock from any context. The remainder > > of the clk API is callable only from contexts where sleeping is permissible. > > > > The reason we have this split is because clk_enable()/clk_disable() have > > historically been used in interrupt handlers, and they're specifically > > not supposed to impose big delays. > > > > Things like waiting for a PLL to re-lock is time-consuming, so it's not > > something I'd expect to see behind a clk_enable() implementation (the > > fact you can't sleep in there is a big hint.) Such waits should be in > > the clk_prepare() stage instead. > > > > Now, as for clk_enable() being interrupted - if clk_enable() is interrupted > > and another clk_enable() comes along for the same clock, that second > > clk_enable() should not return until the clock has actually been enabled, > > and it's up to the implementation to decode how to achieve that. If that > > means a RT implementation using a raw spinlock, then that's one option > > (which basically would have the side effect of blocking until the preempted > > clk_enable() finishes its business.) Alternatively, if we can preempt > > inside clk_enable(), then the clk_enable() implementation should be written > > to cope with that (eg, by the second clk_enable() fiddling with the hardware, > > and the first thread noticing that it has nothing to do.) > > > > Thanks a lot for your comments and explanations. > > Now lock object in CCF is not a raw spinlock, so, seems, I have to update > code and try to move clk_enable()/clk_disable() out of atomic context. clk_enable/clk_disable _should_ be usable from atomic contexts. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
