Re: [PATCH v1 2/2] clk: Add support for sync_state()

[Saravana Kannan]

On Tue, Apr 6, 2021 at 8:45 PM 'Saravana Kannan' via kernel-team
<kernel-team@xxxxxxxxxxx> wrote:
>
> Clocks can be turned on (by the hardware, bootloader, etc) upon a
> reset/boot of a hardware platform. These "boot clocks" could be clocking
> devices that are active before the kernel starts running. For example,
> clocks needed for the interconnects, UART console, display, CPUs, DDR,
> etc.
>
> When a boot clock is used by more than one consumer or multiple boot
> clocks share a parent clock, the boot clock (or the common parent) can
> be turned off when the first consumer probes. This can crash the device
> or cause poor user experience.
>
> Fix this by explicitly enabling the boot clocks during clock
> registration and then removing the enable vote when the clock provider
> device gets its sync_state() callback. Since sync_state() callback comes
> only when all the consumers of a device (not a specific clock) have
> probed, this ensures the boot clocks are kept on at least until all
> their consumers have had a chance to vote on them (in their respective
> probe functions).
>
> Also, if a clock provider is loaded as a module and it has some boot
> clocks, they get turned off only when a consumer explicitly turns them
> off. So clocks that are boot clocks and are unused never get turned off
> because the logic to turn off unused clocks has already run during
> late_initcall_sync(). Adding sync_state() support also makes sure these
> unused boot clocks are turned off once all the consumers have probed.
>
> Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>

Hi Stephen,

Gentle reminder.


-Saravana

> ---
>  drivers/clk/clk.c            | 84 +++++++++++++++++++++++++++++++++++-
>  include/linux/clk-provider.h |  1 +
>  2 files changed, 84 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index d6301a3351f2..cd07f4d1254c 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -72,6 +72,8 @@ struct clk_core {
>         unsigned long           flags;
>         bool                    orphan;
>         bool                    rpm_enabled;
> +       bool                    need_sync;
> +       bool                    boot_enabled;
>         unsigned int            enable_count;
>         unsigned int            prepare_count;
>         unsigned int            protect_count;
> @@ -1215,6 +1217,15 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
>         hlist_for_each_entry(child, &core->children, child_node)
>                 clk_unprepare_unused_subtree(child);
>
> +       /*
> +        * Orphan clocks might still not have their state held if one of their
> +        * ancestors hasn't been registered yet. We don't want to turn off
> +        * these orphan clocks now as they will be turned off later when their
> +        * device gets a sync_state() call.
> +        */
> +       if (dev_has_sync_state(core->dev))
> +               return;
> +
>         if (core->prepare_count)
>                 return;
>
> @@ -1246,6 +1257,15 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>         hlist_for_each_entry(child, &core->children, child_node)
>                 clk_disable_unused_subtree(child);
>
> +       /*
> +        * Orphan clocks might still not have their state held if one of their
> +        * ancestors hasn't been registered yet. We don't want to turn off
> +        * these orphan clocks now as they will be turned off later when their
> +        * device gets a sync_state() call.
> +        */
> +       if (dev_has_sync_state(core->dev))
> +               return;
> +
>         if (core->flags & CLK_OPS_PARENT_ENABLE)
>                 clk_core_prepare_enable(core->parent);
>
> @@ -1319,6 +1339,38 @@ static int __init clk_disable_unused(void)
>  }
>  late_initcall_sync(clk_disable_unused);
>
> +static void clk_unprepare_disable_dev_subtree(struct clk_core *core,
> +                                             struct device *dev)
> +{
> +       struct clk_core *child;
> +
> +       lockdep_assert_held(&prepare_lock);
> +
> +       hlist_for_each_entry(child, &core->children, child_node)
> +               clk_unprepare_disable_dev_subtree(child, dev);
> +
> +       if (core->dev != dev || !core->need_sync)
> +               return;
> +
> +       clk_core_disable_unprepare(core);
> +}
> +
> +void clk_sync_state(struct device *dev)
> +{
> +       struct clk_core *core;
> +
> +       clk_prepare_lock();
> +
> +       hlist_for_each_entry(core, &clk_root_list, child_node)
> +               clk_unprepare_disable_dev_subtree(core, dev);
> +
> +       hlist_for_each_entry(core, &clk_orphan_list, child_node)
> +               clk_unprepare_disable_dev_subtree(core, dev);
> +
> +       clk_prepare_unlock();
> +}
> +EXPORT_SYMBOL_GPL(clk_sync_state);
> +
>  static int clk_core_determine_round_nolock(struct clk_core *core,
>                                            struct clk_rate_request *req)
>  {
> @@ -1725,6 +1777,30 @@ int clk_hw_get_parent_index(struct clk_hw *hw)
>  }
>  EXPORT_SYMBOL_GPL(clk_hw_get_parent_index);
>
> +static void clk_core_hold_state(struct clk_core *core)
> +{
> +       if (core->need_sync || !core->boot_enabled)
> +               return;
> +
> +       if (core->orphan || !dev_has_sync_state(core->dev))
> +               return;
> +
> +       core->need_sync = !clk_core_prepare_enable(core);
> +}
> +
> +static void __clk_core_update_orphan_hold_state(struct clk_core *core)
> +{
> +       struct clk_core *child;
> +
> +       if (core->orphan)
> +               return;
> +
> +       clk_core_hold_state(core);
> +
> +       hlist_for_each_entry(child, &core->children, child_node)
> +               __clk_core_update_orphan_hold_state(child);
> +}
> +
>  /*
>   * Update the orphan status of @core and all its children.
>   */
> @@ -3392,6 +3468,7 @@ static void clk_core_reparent_orphans_nolock(void)
>                         __clk_set_parent_after(orphan, parent, NULL);
>                         __clk_recalc_accuracies(orphan);
>                         __clk_recalc_rates(orphan, 0);
> +                       __clk_core_update_orphan_hold_state(orphan);
>                 }
>         }
>  }
> @@ -3550,6 +3627,8 @@ static int __clk_core_init(struct clk_core *core)
>                 rate = 0;
>         core->rate = core->req_rate = rate;
>
> +       core->boot_enabled = clk_core_is_enabled(core);
> +
>         /*
>          * Enable CLK_IS_CRITICAL clocks so newly added critical clocks
>          * don't get accidentally disabled when walking the orphan tree and
> @@ -3572,6 +3651,7 @@ static int __clk_core_init(struct clk_core *core)
>                 }
>         }
>
> +       clk_core_hold_state(core);
>         clk_core_reparent_orphans_nolock();
>
>
> @@ -3837,8 +3917,10 @@ __clk_register(struct device *dev, struct device_node *np, struct clk_hw *hw)
>                 core->rpm_enabled = true;
>         core->dev = dev;
>         core->of_node = np;
> -       if (dev && dev->driver)
> +       if (dev && dev->driver) {
>                 core->owner = dev->driver->owner;
> +               dev_set_drv_sync_state(dev, clk_sync_state);
> +       }
>         core->hw = hw;
>         core->flags = init->flags;
>         core->num_parents = init->num_parents;
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 58f6fe866ae9..429c413dadce 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -1112,6 +1112,7 @@ void devm_clk_unregister(struct device *dev, struct clk *clk);
>
>  void clk_hw_unregister(struct clk_hw *hw);
>  void devm_clk_hw_unregister(struct device *dev, struct clk_hw *hw);
> +void clk_sync_state(struct device *dev);
>
>  /* helper functions */
>  const char *__clk_get_name(const struct clk *clk);
> --
> 2.31.1.295.g9ea45b61b8-goog
>
> --
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