On Wed, 29 Jul 2015, Michael Turquette wrote: > Hi Lee, > > + linux-clk ml > > Quoting Lee Jones (2015-07-22 06:04:13) > > These new API calls will firstly provide a mechanisms to tag a clock as > > critical and secondly allow any knowledgeable driver to (un)gate clocks, > > even if they are marked as critical. > > > > Suggested-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx> > > --- > > drivers/clk/clk.c | 45 ++++++++++++++++++++++++++++++++++++++++++++ > > include/linux/clk-provider.h | 2 ++ > > include/linux/clk.h | 30 +++++++++++++++++++++++++++++ > > 3 files changed, 77 insertions(+) > > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > > index 61c3fc5..486b1da 100644 > > --- a/drivers/clk/clk.c > > +++ b/drivers/clk/clk.c > > @@ -46,6 +46,21 @@ static struct clk_core *clk_core_lookup(const char *name); > > > > /*** private data structures ***/ > > > > +/** > > + * struct critical - Provides 'play' over critical clocks. A clock can be > > + * marked as critical, meaning that it should not be > > + * disabled. However, if a driver which is aware of the > > + * critical behaviour wants to control it, it can do so > > + * using clk_enable_critical() and clk_disable_critical(). > > + * > > + * @enabled Is clock critical? Once set, doesn't change > > + * @leave_on Self explanatory. Can be disabled by knowledgeable drivers > > Not self explanatory. I need this explained to me. What does leave_on > do? Better yet, what would happen if leave_on did not exist? > > > + */ > > +struct critical { > > + bool enabled; > > + bool leave_on; > > +}; > > + > > struct clk_core { > > const char *name; > > const struct clk_ops *ops; > > @@ -75,6 +90,7 @@ struct clk_core { > > struct dentry *dentry; > > #endif > > struct kref ref; > > + struct critical critical; > > }; > > > > struct clk { > > @@ -995,6 +1011,10 @@ static void clk_core_disable(struct clk_core *clk) > > if (WARN_ON(clk->enable_count == 0)) > > return; > > > > + /* Refuse to turn off a critical clock */ > > + if (clk->enable_count == 1 && clk->critical.leave_on) > > + return; > > How do we get to this point? clk_enable_critical actually calls > clk_enable, thus incrementing the enable_count. The only time that we > could hit the above case is if, > > a) there is an imbalance in clk_enable and clk_disable calls. If this is > the case then the drivers need to be fixed. Or better yet some > infrastructure to catch that, now that we have per-user struct clk > cookies. > > b) a driver knowingly calls clk_enable_critical(foo) and then regular, > old clk_disable(foo). But why would a driver do that? > > It might be that I am missing the point here, so please feel free to > clue me in. This check behaves in a very similar to the WARN() above. It's more of a fail-safe. If all drivers are behaving properly, then it shouldn't ever be true. If they're not, it prevents an incorrectly written driver from irrecoverably crippling the system. As I said in the other mail. We can do without these 3 new wrappers. We _could_ just write a driver which only calls clk_enable() _after_ it calls clk_disable(), a kind of intentional unbalance and it would do that same thing. However, what we're trying to do here is provide a proper API, so we can see at first glance what the 'knowledgeable' driver is trying to do and not have someone attempt to submit a 'fix' which calls clk_enable() or something. > > + > > if (--clk->enable_count > 0) > > return; > > > > @@ -1037,6 +1057,13 @@ void clk_disable(struct clk *clk) > > } > > EXPORT_SYMBOL_GPL(clk_disable); > > > > +void clk_disable_critical(struct clk *clk) > > +{ > > + clk->core->critical.leave_on = false; > > + clk_disable(clk); > > +} > > +EXPORT_SYMBOL_GPL(clk_disable_critical); > > + > > static int clk_core_enable(struct clk_core *clk) > > { > > int ret = 0; > > @@ -1100,6 +1127,15 @@ int clk_enable(struct clk *clk) > > } > > EXPORT_SYMBOL_GPL(clk_enable); > > > > +int clk_enable_critical(struct clk *clk) > > +{ > > + if (clk->core->critical.enabled) > > + clk->core->critical.leave_on = true; > > + > > + return clk_enable(clk); > > +} > > +EXPORT_SYMBOL_GPL(clk_enable_critical); > > + > > static unsigned long clk_core_round_rate_nolock(struct clk_core *clk, > > unsigned long rate, > > unsigned long min_rate, > > @@ -2482,6 +2518,15 @@ fail_out: > > } > > EXPORT_SYMBOL_GPL(clk_register); > > > > +void clk_init_critical(struct clk *clk) > > +{ > > + struct critical *critical = &clk->core->critical; > > + > > + critical->enabled = true; > > + critical->leave_on = true; > > +} > > +EXPORT_SYMBOL_GPL(clk_init_critical); > > + > > /* > > * Free memory allocated for a clock. > > * Caller must hold prepare_lock. > > diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h > > index 5591ea7..15ef8c9 100644 > > --- a/include/linux/clk-provider.h > > +++ b/include/linux/clk-provider.h > > @@ -563,6 +563,8 @@ struct clk *devm_clk_register(struct device *dev, struct clk_hw *hw); > > void clk_unregister(struct clk *clk); > > void devm_clk_unregister(struct device *dev, struct clk *clk); > > > > +void clk_init_critical(struct clk *clk); > > + > > /* helper functions */ > > const char *__clk_get_name(struct clk *clk); > > struct clk_hw *__clk_get_hw(struct clk *clk); > > diff --git a/include/linux/clk.h b/include/linux/clk.h > > index 8381bbf..9807f3b 100644 > > --- a/include/linux/clk.h > > +++ b/include/linux/clk.h > > @@ -231,6 +231,19 @@ struct clk *devm_clk_get(struct device *dev, const char *id); > > int clk_enable(struct clk *clk); > > > > /** > > + * clk_enable_critical - inform the system when the clock source should be > > + * running, even if clock is critical. > > + * @clk: clock source > > + * > > + * If the clock can not be enabled/disabled, this should return success. > > + * > > + * May be called from atomic contexts. > > + * > > + * Returns success (0) or negative errno. > > + */ > > +int clk_enable_critical(struct clk *clk); > > + > > +/** > > * clk_disable - inform the system when the clock source is no longer required. > > * @clk: clock source > > * > > @@ -247,6 +260,23 @@ int clk_enable(struct clk *clk); > > void clk_disable(struct clk *clk); > > > > /** > > + * clk_disable_critical - inform the system when the clock source is no > > + * longer required, even if clock is critical. > > + * @clk: clock source > > + * > > + * Inform the system that a clock source is no longer required by > > + * a driver and may be shut down. > > + * > > + * May be called from atomic contexts. > > + * > > + * Implementation detail: if the clock source is shared between > > + * multiple drivers, clk_enable_critical() calls must be balanced > > + * by the same number of clk_disable_critical() calls for the clock > > + * source to be disabled. > > + */ > > +void clk_disable_critical(struct clk *clk); > > + > > +/** > > * clk_get_rate - obtain the current clock rate (in Hz) for a clock source. > > * This is only valid once the clock source has been enabled. > > * @clk: clock source -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html