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Date: Wed, 24 Oct 2018 13:50:28 -0700 Message-ID: Subject: Re: [PATCH 1/6] clk: Remove recursion in clk_core_{prepare,enable}() To: jbrunet@baylibre.com Cc: linux-kernel , linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-doc@vger.kernel.org, sboyd@kernel.org, Michael Turquette , =?UTF-8?Q?Heiko_St=C3=BCbner?= , aisheng.dong@nxp.com, mchehab+samsung@kernel.org, Jonathan Corbet , Stephen Boyd Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 24, 2018 at 1:15 PM dbasehore . wrote: > > On Wed, Oct 24, 2018 at 2:51 AM Jerome Brunet wrote: > > > > On Tue, 2018-10-23 at 18:31 -0700, Derek Basehore wrote: > > > From: Stephen Boyd > > > > > > 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 > > > > 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 > > > Signed-off-by: Derek Basehore > > > --- > > > 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. > > I think I accidentally messed that up when I picked up the patch. > There were some merge conflicts with the addition of the > clk_pm_runtime code. Nevermind, this is incorrect. The clk_pm_runtime_put is within this if statement too, so there isn't an issue here. > > > > > 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 ? > > No, I think I just accidentally removed this when resolving conflicts. > > > > > > - > > > 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) > > > > Yeah, all of this seems to just be a poor resolution of patch > conflicts on my part. Will fix. Nevermind, that's not the case. We add the first core that has a non-zero prepare_count to the first (or we go all the way to root). That core can't encounter an error since those only happen in the prepare_count == 0 case. If it's NULL, clk_core_unprepare just returns. > > > > 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 */ > > > >