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.) -- 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
