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Date: Thu, 29 Sep 2022 10:10:47 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Abel Vesa <abel.vesa@...aro.org>
Cc: Mike Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...nel.org>,
Bjorn Andersson <bjorn.andersson@...aro.org>,
Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
Konrad Dybcio <konrad.dybcio@...ainline.org>,
linux-clk@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arm-msm@...r.kernel.org
Subject: Re: [RFC 1/2] clk: Add generic sync_state callback for disabling
unused clocks
On Wed, Jul 06, 2022 at 06:04:10PM +0300, Abel Vesa wrote:
> There are unused clocks that need to stay enabled on clk_disable_unused,
> but rather should be disabled later on on sync_state. Provide a generic
> sync_state callback for the clock providers that register such clocks.
> Then, use the same mechanism as clk_disable_unused from that generic
> callback, but pass the device to make sure only the clocks belonging to
> the current clock provider get disabled, if unused. Also, during the
> default clk_disable_unused, if the driver that registered the clock has
> the generic clk_sync_state_disable_unused callback set for sync_state,
> leave its clocks enabled.
>
Overall I like this, just a minor thing about ignoring CLK_IGNORE_UNUSED
from the sync_stat path below.
We've talked about this not being the whole solution, because there
might be devices that will enable/disable clocks that will be used by
later devices. It seems to me that this would be an additional issue
that needs to be fixed - so I don't have a problem with us picking this
up as a first step.
But for boards where this would be a problem there's no longer a way to
opt-out of the disabling of unused clocks. So perhaps we'd want
clk_ignore_unused to affect the sync_state based case as well?
> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> ---
> drivers/clk/clk.c | 67 +++++++++++++++++++++++++++---------
> include/linux/clk-provider.h | 1 +
> 2 files changed, 52 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 7fc191c15507..ea55806505c0 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1218,19 +1218,31 @@ static void clk_core_disable_unprepare(struct clk_core *core)
> clk_core_unprepare_lock(core);
> }
>
> -static void __init clk_unprepare_unused_subtree(struct clk_core *core)
> +static void clk_unprepare_unused_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_unused_subtree(child);
> + clk_unprepare_unused_subtree(child, dev);
> +
> + if (dev && core->dev != dev)
> + return;
> +
> + /*
> + * clock will be unprepared on sync_state,
> + * so leave as is on clk_disable_unused
> + */
> + if (!dev && dev_has_sync_state(core->dev) &&
How about introducing a local variable bool from_sync_state = !!dev, to
make these conditionals easier to read?
> + core->dev->driver->sync_state == clk_sync_state_disable_unused)
> + return;
>
> if (core->prepare_count)
> return;
>
> - if (core->flags & CLK_IGNORE_UNUSED)
> + if (!dev && core->flags & CLK_IGNORE_UNUSED)
Iiuc, when being called from the sync_state path, CLK_IGNORE_UNUSED will
now be ignored (and the clock will be disabled).
We don't have a lot of users of this flag, but would it not make sense
to adhere to this flag even in that case? As a continued means to
describe a clock which shouldn't be automatically disabled...
> return;
>
> if (clk_pm_runtime_get(core))
> @@ -1248,7 +1260,8 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
> clk_pm_runtime_put(core);
> }
>
> -static void __init clk_disable_unused_subtree(struct clk_core *core)
> +static void clk_disable_unused_subtree(struct clk_core *core,
> + struct device *dev)
> {
> struct clk_core *child;
> unsigned long flags;
> @@ -1256,7 +1269,18 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
> lockdep_assert_held(&prepare_lock);
>
> hlist_for_each_entry(child, &core->children, child_node)
> - clk_disable_unused_subtree(child);
> + clk_disable_unused_subtree(child, dev);
> +
> + if (dev && core->dev != dev)
> + return;
> +
> + /*
> + * clock will be disabled on sync_state,
> + * so leave as is on clk_disable_unused
> + */
> + if (!dev && dev_has_sync_state(core->dev) &&
> + core->dev->driver->sync_state == clk_sync_state_disable_unused)
> + return;
>
> if (core->flags & CLK_OPS_PARENT_ENABLE)
> clk_core_prepare_enable(core->parent);
> @@ -1269,7 +1293,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
> if (core->enable_count)
> goto unlock_out;
>
> - if (core->flags & CLK_IGNORE_UNUSED)
> + if (!dev && core->flags & CLK_IGNORE_UNUSED)
> goto unlock_out;
>
> /*
> @@ -1302,35 +1326,46 @@ static int __init clk_ignore_unused_setup(char *__unused)
> }
> __setup("clk_ignore_unused", clk_ignore_unused_setup);
>
> -static int __init clk_disable_unused(void)
> +static void __clk_disable_unused(struct device *dev)
> {
> struct clk_core *core;
>
> - if (clk_ignore_unused) {
> - pr_warn("clk: Not disabling unused clocks\n");
> - return 0;
> - }
As mentioned above, I think it's reasonable to keep this here.
Regards,
Bjorn
> -
> clk_prepare_lock();
>
> hlist_for_each_entry(core, &clk_root_list, child_node)
> - clk_disable_unused_subtree(core);
> + clk_disable_unused_subtree(core, dev);
>
> hlist_for_each_entry(core, &clk_orphan_list, child_node)
> - clk_disable_unused_subtree(core);
> + clk_disable_unused_subtree(core, dev);
>
> hlist_for_each_entry(core, &clk_root_list, child_node)
> - clk_unprepare_unused_subtree(core);
> + clk_unprepare_unused_subtree(core, dev);
>
> hlist_for_each_entry(core, &clk_orphan_list, child_node)
> - clk_unprepare_unused_subtree(core);
> + clk_unprepare_unused_subtree(core, dev);
>
> clk_prepare_unlock();
> +}
> +
> +static int __init clk_disable_unused(void)
> +{
> + if (clk_ignore_unused) {
> + pr_warn("clk: Not disabling unused clocks\n");
> + return 0;
> + }
> +
> + __clk_disable_unused(NULL);
>
> return 0;
> }
> late_initcall_sync(clk_disable_unused);
>
> +void clk_sync_state_disable_unused(struct device *dev)
> +{
> + __clk_disable_unused(dev);
> +}
> +EXPORT_SYMBOL_GPL(clk_sync_state_disable_unused);
> +
> static int clk_core_determine_round_nolock(struct clk_core *core,
> struct clk_rate_request *req)
> {
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 72d937c03a3e..5d3ed2b14f2c 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -679,6 +679,7 @@ struct clk *clk_register_divider_table(struct device *dev, const char *name,
> void __iomem *reg, u8 shift, u8 width,
> u8 clk_divider_flags, const struct clk_div_table *table,
> spinlock_t *lock);
> +void clk_sync_state_disable_unused(struct device *dev);
> /**
> * clk_register_divider - register a divider clock with the clock framework
> * @dev: device registering this clock
> --
> 2.34.3
>
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