On Tue, 2018-10-23 at 18:31 -0700, Derek Basehore wrote: > From: Stephen Boyd <[email protected]> > > Enabling and preparing clocks can be written quite naturally with > recursion. We start at some point in the tree and recurse up the > tree to find the oldest parent clk that needs to be enabled or > prepared. Then we enable/prepare and return to the caller, going > back to the clk we started at and enabling/preparing along the > way. > > The problem is recursion isn't great for kernel code where we > have a limited stack size. Furthermore, we may be calling this > code inside clk_set_rate() which also has recursion in it, so > we're really not looking good if we encounter a tall clk tree. > > Let's create a stack instead by looping over the parent chain and > collecting clks of interest. Then the enable/prepare becomes as > simple as iterating over that list and calling enable.
Hi Derek, What about unprepare() and disable() ? This patch removes the recursion from the enable path but keeps it for the disable path ... this is very odd. Assuming doing so works, It certainly makes CCF a lot harder to understand. What about clock protection which essentially works on the same model as prepare and enable ? Overall, this change does not look like something that should be merged as it is. If you were just seeking comments, you should add the "RFC" tag to your series. Jerome. > > Cc: Jerome Brunet <[email protected]> If you don't mind, I would prefer to get the whole series next time. It helps to get the context. > Signed-off-by: Stephen Boyd <[email protected]> > Signed-off-by: Derek Basehore <[email protected]> > --- > drivers/clk/clk.c | 113 ++++++++++++++++++++++++++-------------------- > 1 file changed, 64 insertions(+), 49 deletions(-) > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > index af011974d4ec..95d818f5edb2 100644 > --- a/drivers/clk/clk.c > +++ b/drivers/clk/clk.c > @@ -71,6 +71,8 @@ struct clk_core { > struct hlist_head children; > struct hlist_node child_node; > struct hlist_head clks; > + struct list_head prepare_list; > + struct list_head enable_list; > unsigned int notifier_count; > #ifdef CONFIG_DEBUG_FS > struct dentry *dentry; > @@ -740,49 +742,48 @@ EXPORT_SYMBOL_GPL(clk_unprepare); > static int clk_core_prepare(struct clk_core *core) > { > int ret = 0; > + struct clk_core *tmp, *parent; > + LIST_HEAD(head); > > lockdep_assert_held(&prepare_lock); > > - if (!core) > - return 0; > + while (core) { > + list_add(&core->prepare_list, &head); > + /* Stop once we see a clk that is already prepared */ > + if (core->prepare_count) > + break; > + core = core->parent; > + } > > - if (core->prepare_count == 0) { > - ret = clk_pm_runtime_get(core); > - if (ret) > - return ret; > + list_for_each_entry_safe(core, tmp, &head, prepare_list) { > + list_del_init(&core->prepare_list); Is there any point in removing it from the list ? Maybe I missed it but it does not seems useful. Without this, we could use list_for_each_entry() > > - ret = clk_core_prepare(core->parent); > - if (ret) > - goto runtime_put; > + if (core->prepare_count == 0) { Should we really check the count here ? You are not checking the count when the put() counterpart is called below. Since PM runtime has ref counting as well, either way would work I guess ... but we shall be consistent > + ret = clk_pm_runtime_get(core); > + if (ret) > + goto err; > > - trace_clk_prepare(core); > + trace_clk_prepare(core); > > - if (core->ops->prepare) > - ret = core->ops->prepare(core->hw); > + if (core->ops->prepare) > + ret = core->ops->prepare(core->hw); > > - trace_clk_prepare_complete(core); > + trace_clk_prepare_complete(core); > > - if (ret) > - goto unprepare; > + if (ret) { > + clk_pm_runtime_put(core); > + goto err; > + } > + } > + core->prepare_count++; > } > > - core->prepare_count++; > - > - /* > - * CLK_SET_RATE_GATE is a special case of clock protection > - * Instead of a consumer claiming exclusive rate control, it is > - * actually the provider which prevents any consumer from making any > - * operation which could result in a rate change or rate glitch while > - * the clock is prepared. > - */ > - if (core->flags & CLK_SET_RATE_GATE) > - clk_core_rate_protect(core); This gets removed without anything replacing it. is CLK_SET_RATE_GATE and clock protection support dropped after this change ? > - > return 0; > -unprepare: > - clk_core_unprepare(core->parent); > -runtime_put: > - clk_pm_runtime_put(core); > +err: > + parent = core->parent; > + list_for_each_entry_safe_continue(core, tmp, &head, prepare_list) > + list_del_init(&core->prepare_list); > + clk_core_unprepare(parent); If you get here because of failure clk_pm_runtime_get(), you will unprepare a clock which may have not been prepared first Overall the rework of error exit path does not seem right (or necessary) > return ret; > } > > @@ -878,37 +879,49 @@ EXPORT_SYMBOL_GPL(clk_disable); > static int clk_core_enable(struct clk_core *core) > { > int ret = 0; > + struct clk_core *tmp, *parent; > + LIST_HEAD(head); > > lockdep_assert_held(&enable_lock); > > - if (!core) > - return 0; > - > - if (WARN(core->prepare_count == 0, > - "Enabling unprepared %s\n", core->name)) > - return -ESHUTDOWN; > + while (core) { > + list_add(&core->enable_list, &head); > + /* Stop once we see a clk that is already enabled */ > + if (core->enable_count) > + break; > + core = core->parent; > + } > > - if (core->enable_count == 0) { > - ret = clk_core_enable(core->parent); > + list_for_each_entry_safe(core, tmp, &head, enable_list) { > + list_del_init(&core->enable_list); > > - if (ret) > - return ret; > + if (WARN_ON(core->prepare_count == 0)) { > + ret = -ESHUTDOWN; > + goto err; > + } > > - trace_clk_enable_rcuidle(core); > + if (core->enable_count == 0) { > + trace_clk_enable_rcuidle(core); > > - if (core->ops->enable) > - ret = core->ops->enable(core->hw); > + if (core->ops->enable) > + ret = core->ops->enable(core->hw); > > - trace_clk_enable_complete_rcuidle(core); > + trace_clk_enable_complete_rcuidle(core); > > - if (ret) { > - clk_core_disable(core->parent); > - return ret; > + if (ret) > + goto err; > } > + > + core->enable_count++; > } > > - core->enable_count++; > return 0; > +err: > + parent = core->parent; > + list_for_each_entry_safe_continue(core, tmp, &head, enable_list) > + list_del_init(&core->enable_list); > + clk_core_disable(parent); > + return ret; > } > > static int clk_core_enable_lock(struct clk_core *core) > @@ -3281,6 +3294,8 @@ struct clk *clk_register(struct device *dev, struct > clk_hw *hw) > core->num_parents = hw->init->num_parents; > core->min_rate = 0; > core->max_rate = ULONG_MAX; > + INIT_LIST_HEAD(&core->prepare_list); > + INIT_LIST_HEAD(&core->enable_list); > hw->core = core; > > /* allocate local copy in case parent_names is __initdata */
