Hi, Am Freitag, 4. August 2017, 16:07:01 CEST schrieb Boris Brezillon: > +Stephen, Mike and the linux-clk ML. > > On Fri, 4 Aug 2017 20:45:04 +0800 > "David.Wu" <david.wu at rock-chips.com> wrote: > > > Hi Boris & Heiko, > > > > ? 2016/3/31 4:03, Boris BREZILLON ??: > > > + /* Keep the PWM clk enabled if the PWM appears to be up and running. */ > > > + pwm_get_state(pc->chip.pwms, &pstate); > > > + if (!pstate.enabled) > > > + clk_disable(pc->clk); > > > > We found a issue recently, if the pwm0 is not enabled at uboot and pwm2 > > is enabled at uboot, the PWM clock will be disabled at pwm0's probe. It > > is true to close the pwm clock, and the pwm2 can't work during a while, > > until the pwm2 probe, because the pwm0 and pwm2 are the same clock for > > their work. In fact, the pwm0 can not know the pwm2's status. > > > > So we need to get all the PWMs state in a public place where it's early > > than the PWM probe, if that's the way it is. Then keep the PWM clk > > enabled if theis is one PWM appears to be up and running. The place > > maybe in the clock core init, like adding pwm clock as critial one. > > > > Another way is that we don't enable pwm clock firstly at PWM probe, > > because whether or not the PWM state has been enabled in the Uboot, like > > other modules, our chip default PWM clock registers are enabled at the > > beginning, read the PWM registers directly to know the PWM state. Then > > if the PWM state is enabled, call the enable_clk(pc->clk) to add the > > clock count=1. If the PWM state is disabled, we do nothing. After all > > the PWMs are probed and all modules are probed, the clock core will gate > > the PWM clock if the clock count is 0, and keep clk enabled if the clock > > count is not 0. > > > > How do you feel about it? > > Ouch. That's indeed hard to solve in a clean way. I may have > something to suggest but I'm not sure clk maintainers will like it: what > if we make clk_disable() and clk_unprepare() just decrement the refcount > before the disable-unused-clks procedure has been executed (see > proposed patch below)? This way all clks that have been enabled by the > bootloader will stay in such state until all drivers have had a chance > to retain them (IOW, call clk_prepare()+clk_enable()). > > BTW, I think the problem you're describing here is not unique to PWM > devices, it's just that now, some PWM drivers are smart and try to keep > clks enabled to prevent glitches. Actually, Mike had patches that introduced so called "handoff" clocks [0]. Clocks that were handled as critical until some driver picked them up. It's not exactly the same as your change and still would require intervention from clock-drivers to mark clocks in such a way. So I really also like your approach, as it would make clock wiggling during early boot safe for everyone involved :-) . And both seem to cater to slightly different use-cases as well. Heiko [0] https://lwn.net/Articles/675658/ > --->8--- > From 47dcdc1bcc30b3ae1f76d33be824d2519a4dcca8 Mon Sep 17 00:00:00 2001 > From: Boris Brezillon <boris.brezillon at free-electrons.com> > Date: Fri, 4 Aug 2017 15:55:49 +0200 > Subject: [PATCH] clk: Keep clocks in their initial state until > clk_disable_unused() is called > > Some drivers are briefly preparing+enabling the clock in their > ->probe() hook and disable+unprepare them before leaving the function. > > This can be problem if a clock is shared between different devices, and > one of these devices is critical to the system. If this clock is > enabled/disabled by a non-critical device before the driver of the > critical one had a chance to enable+prepare it, there might be a short > period of time during which the critical device is not clocked. > > To solve this problem, we save the initial clock state (at registration > time) and prevent the clock from being disabled until kernel init is done > (which is when clk_disable_unused() is called). > > Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com> > --- > drivers/clk/clk.c | 29 +++++++++++++++++++++++++++-- > 1 file changed, 27 insertions(+), 2 deletions(-) > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > index fc58c52a26b4..3f61374a364b 100644 > --- a/drivers/clk/clk.c > +++ b/drivers/clk/clk.c > @@ -58,6 +58,8 @@ struct clk_core { > struct clk_core *new_child; > unsigned long flags; > bool orphan; > + bool keep_enabled; > + bool keep_prepared; > unsigned int enable_count; > unsigned int prepare_count; > unsigned long min_rate; > @@ -486,7 +488,7 @@ static void clk_core_unprepare(struct clk_core *core) > > trace_clk_unprepare(core); > > - if (core->ops->unprepare) > + if (core->ops->unprepare && !core->keep_prepared) > core->ops->unprepare(core->hw); > > trace_clk_unprepare_complete(core); > @@ -602,7 +604,7 @@ static void clk_core_disable(struct clk_core *core) > > trace_clk_disable_rcuidle(core); > > - if (core->ops->disable) > + if (core->ops->disable && !core->keep_enabled) > core->ops->disable(core->hw); > > trace_clk_disable_complete_rcuidle(core); > @@ -739,6 +741,12 @@ static void clk_unprepare_unused_subtree(struct clk_core *core) > hlist_for_each_entry(child, &core->children, child_node) > clk_unprepare_unused_subtree(child); > > + /* > + * Reset the ->keep_prepared flag so that subsequent calls to > + * clk_unprepare() on this clk actually unprepare it. > + */ > + core->keep_prepared = false; > + > if (core->prepare_count) > return; > > @@ -770,6 +778,12 @@ static void clk_disable_unused_subtree(struct clk_core *core) > > flags = clk_enable_lock(); > > + /* > + * Reset the ->keep_enabled flag so that subsequent calls to > + * clk_disable() on this clk actually disable it. > + */ > + core->keep_enabled = false; > + > if (core->enable_count) > goto unlock_out; > > @@ -2446,6 +2460,17 @@ static int __clk_core_init(struct clk_core *core) > core->accuracy = 0; > > /* > + * We keep track of the initial clk status to keep clks in the state > + * they were left in by the bootloader until all drivers had a chance > + * to keep them prepared/enabled if they need to. > + */ > + if (core->ops->is_prepared && !clk_ignore_unused) > + core->keep_prepared = core->ops->is_prepared(core->hw); > + > + if (core->ops->is_enabled && !clk_ignore_unused) > + core->keep_enabled = core->ops->is_enabled(core->hw); > + > + /* > * Set clk's phase. > * Since a phase is by definition relative to its parent, just > * query the current clock phase, or just assume it's in phase. > >
