[v3,2/3] clk: Add clk_poll_disable_unprepare()

Commit Message

Biju Das March 18, 2024, 11:08 a.m. UTC

The clk_disable_unprepare() doesn't guarantee that a clock is gated after
the execution as it is driver dependent. The Renesas and most of the other
platforms don't wait until clock is stopped because of performance reason.
But these platforms wait while turning on the clock.

The normal case for shutting down the clock is unbind/close/suspend or
error paths in the driver. Not waiting for the shutting down the clock
will improve the suspend time.

But on RZ/G2L Camera Data Receiving Unit (CRU) IP, initially the vclk is
on. Before enabling link reception, we need to wait for vclk to be off
and after enabling reception, we need to turn the vlck on. Special cases
like this requires a sync API for clock gating.

Add clk_poll_disable_unprepare() to poll the clock gate operation that
guarantees gating of clk after the execution.

Signed-off-by: Biju Das <[e-mail]>
---
v2->v3:
 * Added WARN_ON(enable count non-zero) and return an error code (-EBUSY),
   if the user is not the sole user of the clock and the enable count is
   non-zero.
 * Returned an error if there's no is_enabled() callback.
RFC->v2:
 * Renamed clk_disable_unprepare_sync()-->clk_poll_disable_unprepare()
 * Redesigned to make use of __clk_is_enabled() to poll the clock gating.
---
 drivers/clk/clk.c   | 29 ++++++++++++++++++++++++++++
 include/linux/clk.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

Comments

Sakari Ailus March 18, 2024, 6:23 p.m. UTC | #1

Hi Biju,

Thanks for the update.

On Mon, Mar 18, 2024 at 11:08:41AM +0000, Biju Das wrote:
> The clk_disable_unprepare() doesn't guarantee that a clock is gated after
> the execution as it is driver dependent. The Renesas and most of the other
> platforms don't wait until clock is stopped because of performance reason.
> But these platforms wait while turning on the clock.
> 
> The normal case for shutting down the clock is unbind/close/suspend or
> error paths in the driver. Not waiting for the shutting down the clock
> will improve the suspend time.
> 
> But on RZ/G2L Camera Data Receiving Unit (CRU) IP, initially the vclk is
> on. Before enabling link reception, we need to wait for vclk to be off
> and after enabling reception, we need to turn the vlck on. Special cases
> like this requires a sync API for clock gating.
> 
> Add clk_poll_disable_unprepare() to poll the clock gate operation that
> guarantees gating of clk after the execution.
> 
> Signed-off-by: Biju Das <[e-mail]>
> ---
> v2->v3:
>  * Added WARN_ON(enable count non-zero) and return an error code (-EBUSY),
>    if the user is not the sole user of the clock and the enable count is
>    non-zero.
>  * Returned an error if there's no is_enabled() callback.
> RFC->v2:
>  * Renamed clk_disable_unprepare_sync()-->clk_poll_disable_unprepare()
>  * Redesigned to make use of __clk_is_enabled() to poll the clock gating.
> ---
>  drivers/clk/clk.c   | 29 ++++++++++++++++++++++++++++
>  include/linux/clk.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index f5fa91a339d7..e10bb14c904d 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -13,6 +13,7 @@
>  #include <linux/mutex.h>
>  #include <linux/spinlock.h>
>  #include <linux/err.h>
> +#include <linux/iopoll.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
>  #include <linux/of.h>
> @@ -1160,6 +1161,34 @@ void clk_disable(struct clk *clk)
>  }
>  EXPORT_SYMBOL_GPL(clk_disable);
>  
> +/**
> + * clk_poll_disabled - poll for clock gating.
> + * @clk: the clk that is going to stop
> + * @sleep_us: Maximum time to sleep between reads in us (0
> + *            tight-loops).  Should be less than ~20ms since usleep_range
> + *            is used (see Documentation/timers/timers-howto.rst).
> + * @timeout_us: Timeout in us, 0 means never timeout
> + *
> + * It polls for a clk to be stopped.
> + */

We should have documentation either in the header or here, not both. I'd
drop this.

> +int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64 timeout_us)
> +{
> +	bool status;
> +
> +	if (IS_ERR_OR_NULL(clk))
> +		return 0;
> +
> +	if (!clk->core->ops->is_enabled)
> +		return -EOPNOTSUPP;
> +
> +	if (WARN(__clk_get_enable_count(clk), "clk is in use\n"))
> +		return -EBUSY;
> +
> +	return read_poll_timeout(__clk_is_enabled, status, !status, sleep_us,
> +				 timeout_us, false, clk);
> +}
> +EXPORT_SYMBOL_GPL(clk_poll_disabled);
> +
>  static int clk_core_enable(struct clk_core *core)
>  {
>  	int ret = 0;
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index 84b02518791f..7f714ecce0eb 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -693,6 +693,20 @@ int __must_check clk_bulk_enable(int num_clks,
>   */
>  void clk_disable(struct clk *clk);
>  
> +/**
> + * clk_poll_disabled - inform the system whether the clock source is stopped.
> + * @clk: clock source
> + * @sleep_us: Maximum time to sleep between reads in us (0
> + *            tight-loops).  Should be less than ~20ms since usleep_range
> + *            is used (see Documentation/timers/timers-howto.rst).
> + * @timeout_us: Timeout in us, 0 means never timeout
> + *
> + * Poll for clock gating and Inform the system about it's status.

How about, instead:

	Poll for clock gating and return when either there's a timeout or
	the clock has been gated.

	Returns: 0 if the clock is successfully gated, error otherwise.

Please run scripts/kerneldoc -Wall on this.

> + *
> + * Context: May sleep.
> + */
> +int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64 timeout_us);
> +
>  /**
>   * clk_bulk_disable - inform the system when the set of clks is no
>   *		      longer required.
> @@ -1030,6 +1044,11 @@ static inline int __must_check clk_bulk_enable(int num_clks,
>  
>  static inline void clk_disable(struct clk *clk) {}
>  
> +static inline int clk_poll_disabled(struct clk *clk, unsigned long sleep_us,
> +				    u64 timeout_us)
> +{
> +	return 0;
> +}
>  
>  static inline void clk_bulk_disable(int num_clks,
>  				    const struct clk_bulk_data *clks) {}
> @@ -1121,6 +1140,33 @@ static inline void clk_disable_unprepare(struct clk *clk)
>  	clk_unprepare(clk);
>  }
>  
> +/**
> + * clk_poll_disable_unprepare - Poll clk_disable_unprepare

How about calling this clk_disable_sync_unprepare?

I'm not sure if a special function is needed for something needed so rarely
as you can already call clk_poll_disabled(). Maybe others have an opinion
on this, too.

> + * @clk: clock source
> + * @sleep_us: Maximum time to sleep between reads in us (0
> + *            tight-loops).  Should be less than ~20ms since usleep_range
> + *            is used (see Documentation/timers/timers-howto.rst).
> + * @timeout_us: Timeout in us, 0 means never timeout
> + *
> + * Context: May sleep.
> + *
> + * This function polls until the clock has stopped.
> + *
> + * Returns success (0) or negative errno.
> + */
> +static inline int clk_poll_disable_unprepare(struct clk *clk,
> +					     unsigned long sleep_us,
> +					     u64 timeout_us)
> +{
> +	int ret;
> +
> +	clk_disable(clk);
> +	ret = clk_poll_disabled(clk, sleep_us, timeout_us);
> +	clk_unprepare(clk);
> +
> +	return ret;
> +}
> +
>  static inline int __must_check
>  clk_bulk_prepare_enable(int num_clks, const struct clk_bulk_data *clks)
>  {

Laurent Pinchart March 18, 2024, 10:55 p.m. UTC | #2

Hi Biju,

Thank you for the patch.

On Mon, Mar 18, 2024 at 11:08:41AM +0000, Biju Das wrote:
> The clk_disable_unprepare() doesn't guarantee that a clock is gated after
> the execution as it is driver dependent. The Renesas and most of the other
> platforms don't wait until clock is stopped because of performance reason.

Is that really the case for most platforms ? I've never seen that being
an issue in practice.

> But these platforms wait while turning on the clock.
> 
> The normal case for shutting down the clock is unbind/close/suspend or
> error paths in the driver. Not waiting for the shutting down the clock
> will improve the suspend time.
> 
> But on RZ/G2L Camera Data Receiving Unit (CRU) IP, initially the vclk is
> on. Before enabling link reception, we need to wait for vclk to be off
> and after enabling reception, we need to turn the vlck on. Special cases
> like this requires a sync API for clock gating.
> 
> Add clk_poll_disable_unprepare() to poll the clock gate operation that
> guarantees gating of clk after the execution.
> 
> Signed-off-by: Biju Das <[e-mail]>
> ---
> v2->v3:
>  * Added WARN_ON(enable count non-zero) and return an error code (-EBUSY),
>    if the user is not the sole user of the clock and the enable count is
>    non-zero.
>  * Returned an error if there's no is_enabled() callback.
> RFC->v2:
>  * Renamed clk_disable_unprepare_sync()-->clk_poll_disable_unprepare()
>  * Redesigned to make use of __clk_is_enabled() to poll the clock gating.
> ---
>  drivers/clk/clk.c   | 29 ++++++++++++++++++++++++++++
>  include/linux/clk.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index f5fa91a339d7..e10bb14c904d 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -13,6 +13,7 @@
>  #include <linux/mutex.h>
>  #include <linux/spinlock.h>
>  #include <linux/err.h>
> +#include <linux/iopoll.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
>  #include <linux/of.h>
> @@ -1160,6 +1161,34 @@ void clk_disable(struct clk *clk)
>  }
>  EXPORT_SYMBOL_GPL(clk_disable);
>  
> +/**
> + * clk_poll_disabled - poll for clock gating.
> + * @clk: the clk that is going to stop
> + * @sleep_us: Maximum time to sleep between reads in us (0
> + *            tight-loops).  Should be less than ~20ms since usleep_range
> + *            is used (see Documentation/timers/timers-howto.rst).
> + * @timeout_us: Timeout in us, 0 means never timeout
> + *
> + * It polls for a clk to be stopped.
> + */
> +int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64 timeout_us)
> +{
> +	bool status;
> +
> +	if (IS_ERR_OR_NULL(clk))
> +		return 0;
> +
> +	if (!clk->core->ops->is_enabled)
> +		return -EOPNOTSUPP;
> +
> +	if (WARN(__clk_get_enable_count(clk), "clk is in use\n"))
> +		return -EBUSY;

A WARN() is fairly bad, given how easy it could be to this this
condition. To make it safe in the genral case for drivers to use this
API, we may need a way to acquire a clock exclusively, which would
complexify the API quite a bit.

> +
> +	return read_poll_timeout(__clk_is_enabled, status, !status, sleep_us,
> +				 timeout_us, false, clk);
> +}
> +EXPORT_SYMBOL_GPL(clk_poll_disabled);
> +
>  static int clk_core_enable(struct clk_core *core)
>  {
>  	int ret = 0;
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index 84b02518791f..7f714ecce0eb 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -693,6 +693,20 @@ int __must_check clk_bulk_enable(int num_clks,
>   */
>  void clk_disable(struct clk *clk);
>  
> +/**
> + * clk_poll_disabled - inform the system whether the clock source is stopped.
> + * @clk: clock source
> + * @sleep_us: Maximum time to sleep between reads in us (0
> + *            tight-loops).  Should be less than ~20ms since usleep_range
> + *            is used (see Documentation/timers/timers-howto.rst).
> + * @timeout_us: Timeout in us, 0 means never timeout
> + *
> + * Poll for clock gating and Inform the system about it's status.
> + *
> + * Context: May sleep.
> + */
> +int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64 timeout_us);
> +
>  /**
>   * clk_bulk_disable - inform the system when the set of clks is no
>   *		      longer required.
> @@ -1030,6 +1044,11 @@ static inline int __must_check clk_bulk_enable(int num_clks,
>  
>  static inline void clk_disable(struct clk *clk) {}
>  
> +static inline int clk_poll_disabled(struct clk *clk, unsigned long sleep_us,
> +				    u64 timeout_us)
> +{
> +	return 0;
> +}
>  
>  static inline void clk_bulk_disable(int num_clks,
>  				    const struct clk_bulk_data *clks) {}
> @@ -1121,6 +1140,33 @@ static inline void clk_disable_unprepare(struct clk *clk)
>  	clk_unprepare(clk);
>  }
>  
> +/**
> + * clk_poll_disable_unprepare - Poll clk_disable_unprepare
> + * @clk: clock source
> + * @sleep_us: Maximum time to sleep between reads in us (0
> + *            tight-loops).  Should be less than ~20ms since usleep_range
> + *            is used (see Documentation/timers/timers-howto.rst).
> + * @timeout_us: Timeout in us, 0 means never timeout
> + *
> + * Context: May sleep.
> + *
> + * This function polls until the clock has stopped.
> + *
> + * Returns success (0) or negative errno.
> + */
> +static inline int clk_poll_disable_unprepare(struct clk *clk,
> +					     unsigned long sleep_us,
> +					     u64 timeout_us)
> +{
> +	int ret;
> +
> +	clk_disable(clk);
> +	ret = clk_poll_disabled(clk, sleep_us, timeout_us);
> +	clk_unprepare(clk);

What happens in the clk_disable_unprepare() case, if the clk_unprepare()
function is called on a clock that hasn't been synchronously disabled ?
This is ill-defined, a clock provider driver that implements .disable()
asynchronously would see its .unprepare() operation called with
different clock states. That behaviour is error-prone, especially given
that it could be difficult to test clock provider drivers to ensure that
handle both cases correctly.

One option could be to turn the .unprepare() operation into a
synchronization point, requiring drivers that implement .disable()
asynchronously to implement synchronization in .unprepare(). That way
you wouldn't need a new API function for clock consumers. The downside
is that consumers that call clk_disable_unprepare() will never benefit
from the .disable() operation being asynchronous, which may defeat the
whole point of this exercise.

I'm starting to wonder if the simplest option in your case wouldn't be
to make your clock provider synchronous for the vclk...

> +
> +	return ret;
> +}
> +
>  static inline int __must_check
>  clk_bulk_prepare_enable(int num_clks, const struct clk_bulk_data *clks)
>  {

Stephen Boyd April 11, 2024, 8:12 a.m. UTC | #3

Quoting Laurent Pinchart (2024-03-18 15:55:46)
> On Mon, Mar 18, 2024 at 11:08:41AM +0000, Biju Das wrote:
> > +     int ret;
> > +
> > +     clk_disable(clk);
> > +     ret = clk_poll_disabled(clk, sleep_us, timeout_us);
> > +     clk_unprepare(clk);
> 
> What happens in the clk_disable_unprepare() case, if the clk_unprepare()
> function is called on a clock that hasn't been synchronously disabled ?
> This is ill-defined, a clock provider driver that implements .disable()
> asynchronously would see its .unprepare() operation called with
> different clock states. That behaviour is error-prone, especially given
> that it could be difficult to test clock provider drivers to ensure that
> handle both cases correctly.
> 
> One option could be to turn the .unprepare() operation into a
> synchronization point, requiring drivers that implement .disable()
> asynchronously to implement synchronization in .unprepare(). That way
> you wouldn't need a new API function for clock consumers. The downside
> is that consumers that call clk_disable_unprepare() will never benefit
> from the .disable() operation being asynchronous, which may defeat the
> whole point of this exercise.
> 
> I'm starting to wonder if the simplest option in your case wouldn't be
> to make your clock provider synchronous for the vclk...

Yes. This all looks unnecessary if the device using the clk always
requires the clk to actually be shut down when it is disabled. Just do
that for this vclk and move on. It _is_ tightly coupling this specific
clk to the specific consumer, but that's simplest and most expedient to
implement, i.e. it's practical.

We would only ever need this API if we had a clk consumer which
absolutely required the clk to stop clocking upon returning from
clk_unprepare(), and that clk could be any random clk. It sounds like in
this case that isn't true. We know which clk must be off when
clk_unprepare() returns, so just implement the wait in the
clk_ops::unprepare() callback?

Russell King (Oracle) April 12, 2024, 3:41 p.m. UTC | #4

On Mon, Mar 18, 2024 at 11:08:41AM +0000, Biju Das wrote:
> The clk_disable_unprepare() doesn't guarantee that a clock is gated after
> the execution as it is driver dependent. The Renesas and most of the other
> platforms don't wait until clock is stopped because of performance reason.

I'm not sure it's "because of performance reason". It's probably more
that it's not important for functionality.

> But these platforms wait while turning on the clock.
> 
> The normal case for shutting down the clock is unbind/close/suspend or
> error paths in the driver. Not waiting for the shutting down the clock
> will improve the suspend time.
> 
> But on RZ/G2L Camera Data Receiving Unit (CRU) IP, initially the vclk is
> on. Before enabling link reception, we need to wait for vclk to be off
> and after enabling reception, we need to turn the vlck on. Special cases

"vclk" not "vlck".

> like this requires a sync API for clock gating.

I suppose this is fine for clocks that only have a single user, but
this is highly undefined for clocks that could be shared between
several different users, since it becomes racy whether another user
of the clock has enabled or disabled this clock.

I think this new API needs to spell it that it is not for clocks
that are shared.

Biju Das June 1, 2024, 7:40 a.m. UTC | #5

Hi Russell King,

Thanks for the feedback.

> -----Original Message-----
> From: Russell King <[e-mail]>
> Sent: Friday, April 12, 2024 4:41 PM
> Subject: Re: [PATCH v3 2/3] clk: Add clk_poll_disable_unprepare()
> 
> On Mon, Mar 18, 2024 at 11:08:41AM +0000, Biju Das wrote:
> > The clk_disable_unprepare() doesn't guarantee that a clock is gated
> > after the execution as it is driver dependent. The Renesas and most of
> > the other platforms don't wait until clock is stopped because of performance reason.
> 
> I'm not sure it's "because of performance reason". It's probably more that it's not important for
> functionality.

Yes, It is not important for functionality. I mean "performance reason" because
the system can enter into suspend state very quickly and thereby saving the power 
of the whole system during suspend process(as we don't need to poll for turning
off each clock during suspend as it is not important).

> 
> > But these platforms wait while turning on the clock.
> >
> > The normal case for shutting down the clock is unbind/close/suspend or
> > error paths in the driver. Not waiting for the shutting down the clock
> > will improve the suspend time.
> >
> > But on RZ/G2L Camera Data Receiving Unit (CRU) IP, initially the vclk
> > is on. Before enabling link reception, we need to wait for vclk to be
> > off and after enabling reception, we need to turn the vlck on. Special
> > cases
> 
> "vclk" not "vlck".

Will fix this in next version.

> 
> > like this requires a sync API for clock gating.
> 
> I suppose this is fine for clocks that only have a single user, but this is highly undefined for
> clocks that could be shared between several different users, since it becomes racy whether another
> user of the clock has enabled or disabled this clock.

Agreed.
> 
> I think this new API needs to spell it that it is not for clocks that are shared.

Will document the new API for exclusive use.

Cheers,
Biju

Biju Das June 1, 2024, 8:05 a.m. UTC | #6

Hi Sakari Ailus,

Thanks for the feedback.

> -----Original Message-----
> From: Sakari Ailus <[e-mail]>
> Sent: Monday, March 18, 2024 6:24 PM
> Subject: Re: [PATCH v3 2/3] clk: Add clk_poll_disable_unprepare()
> 
> Hi Biju,
> 
> Thanks for the update.
> 
> On Mon, Mar 18, 2024 at 11:08:41AM +0000, Biju Das wrote:
> > The clk_disable_unprepare() doesn't guarantee that a clock is gated
> > after the execution as it is driver dependent. The Renesas and most of
> > the other platforms don't wait until clock is stopped because of performance reason.
> > But these platforms wait while turning on the clock.
> >
> > The normal case for shutting down the clock is unbind/close/suspend or
> > error paths in the driver. Not waiting for the shutting down the clock
> > will improve the suspend time.
> >
> > But on RZ/G2L Camera Data Receiving Unit (CRU) IP, initially the vclk
> > is on. Before enabling link reception, we need to wait for vclk to be
> > off and after enabling reception, we need to turn the vlck on. Special
> > cases like this requires a sync API for clock gating.
> >
> > Add clk_poll_disable_unprepare() to poll the clock gate operation that
> > guarantees gating of clk after the execution.
> >
> > Signed-off-by: Biju Das <[e-mail]>
> > ---
> > v2->v3:
> >  * Added WARN_ON(enable count non-zero) and return an error code (-EBUSY),
> >    if the user is not the sole user of the clock and the enable count is
> >    non-zero.
> >  * Returned an error if there's no is_enabled() callback.
> > RFC->v2:
> >  * Renamed clk_disable_unprepare_sync()-->clk_poll_disable_unprepare()
> >  * Redesigned to make use of __clk_is_enabled() to poll the clock gating.
> > ---
> >  drivers/clk/clk.c   | 29 ++++++++++++++++++++++++++++
> >  include/linux/clk.h | 46
> > +++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 75 insertions(+)
> >
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index
> > f5fa91a339d7..e10bb14c904d 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -13,6 +13,7 @@
> >  #include <linux/mutex.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/err.h>
> > +#include <linux/iopoll.h>
> >  #include <linux/list.h>
> >  #include <linux/slab.h>
> >  #include <linux/of.h>
> > @@ -1160,6 +1161,34 @@ void clk_disable(struct clk *clk)  }
> > EXPORT_SYMBOL_GPL(clk_disable);
> >
> > +/**
> > + * clk_poll_disabled - poll for clock gating.
> > + * @clk: the clk that is going to stop
> > + * @sleep_us: Maximum time to sleep between reads in us (0
> > + *            tight-loops).  Should be less than ~20ms since usleep_range
> > + *            is used (see Documentation/timers/timers-howto.rst).
> > + * @timeout_us: Timeout in us, 0 means never timeout
> > + *
> > + * It polls for a clk to be stopped.
> > + */
> 
> We should have documentation either in the header or here, not both. I'd drop this.

OK, will drop from here, If it is ok for every one.
> 
> > +int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64
> > +timeout_us) {
> > +	bool status;
> > +
> > +	if (IS_ERR_OR_NULL(clk))
> > +		return 0;
> > +
> > +	if (!clk->core->ops->is_enabled)
> > +		return -EOPNOTSUPP;
> > +
> > +	if (WARN(__clk_get_enable_count(clk), "clk is in use\n"))
> > +		return -EBUSY;
> > +
> > +	return read_poll_timeout(__clk_is_enabled, status, !status, sleep_us,
> > +				 timeout_us, false, clk);
> > +}
> > +EXPORT_SYMBOL_GPL(clk_poll_disabled);
> > +
> >  static int clk_core_enable(struct clk_core *core)  {
> >  	int ret = 0;
> > diff --git a/include/linux/clk.h b/include/linux/clk.h index
> > 84b02518791f..7f714ecce0eb 100644
> > --- a/include/linux/clk.h
> > +++ b/include/linux/clk.h
> > @@ -693,6 +693,20 @@ int __must_check clk_bulk_enable(int num_clks,
> >   */
> >  void clk_disable(struct clk *clk);
> >
> > +/**
> > + * clk_poll_disabled - inform the system whether the clock source is stopped.
> > + * @clk: clock source
> > + * @sleep_us: Maximum time to sleep between reads in us (0
> > + *            tight-loops).  Should be less than ~20ms since usleep_range
> > + *            is used (see Documentation/timers/timers-howto.rst).
> > + * @timeout_us: Timeout in us, 0 means never timeout
> > + *
> > + * Poll for clock gating and Inform the system about it's status.
> 
> How about, instead:
> 
> 	Poll for clock gating and return when either there's a timeout or
> 	the clock has been gated.
> 
> 	Returns: 0 if the clock is successfully gated, error otherwise.
> 
> Please run scripts/kerneldoc -Wall on this.

OK.

> 
> > + *
> > + * Context: May sleep.
> > + */
> > +int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64
> > +timeout_us);
> > +
> >  /**
> >   * clk_bulk_disable - inform the system when the set of clks is no
> >   *		      longer required.
> > @@ -1030,6 +1044,11 @@ static inline int __must_check
> > clk_bulk_enable(int num_clks,
> >
> >  static inline void clk_disable(struct clk *clk) {}
> >
> > +static inline int clk_poll_disabled(struct clk *clk, unsigned long sleep_us,
> > +				    u64 timeout_us)
> > +{
> > +	return 0;
> > +}
> >
> >  static inline void clk_bulk_disable(int num_clks,
> >  				    const struct clk_bulk_data *clks) {} @@ -1121,6 +1140,33 @@
> > static inline void clk_disable_unprepare(struct clk *clk)
> >  	clk_unprepare(clk);
> >  }
> >
> > +/**
> > + * clk_poll_disable_unprepare - Poll clk_disable_unprepare
> 
> How about calling this clk_disable_sync_unprepare?
> 
> I'm not sure if a special function is needed for something needed so rarely as you can already call
> clk_poll_disabled(). Maybe others have an opinion on this, too.

This API is only for exclusive use. I am ok for clk_disable_sync_unprepare()
as it synchronize clk disable operation first and then call unprepared.

Cheers,
Biju

> 
> > + * @clk: clock source
> > + * @sleep_us: Maximum time to sleep between reads in us (0
> > + *            tight-loops).  Should be less than ~20ms since usleep_range
> > + *            is used (see Documentation/timers/timers-howto.rst).
> > + * @timeout_us: Timeout in us, 0 means never timeout
> > + *
> > + * Context: May sleep.
> > + *
> > + * This function polls until the clock has stopped.
> > + *
> > + * Returns success (0) or negative errno.
> > + */
> > +static inline int clk_poll_disable_unprepare(struct clk *clk,
> > +					     unsigned long sleep_us,
> > +					     u64 timeout_us)
> > +{
> > +	int ret;
> > +
> > +	clk_disable(clk);
> > +	ret = clk_poll_disabled(clk, sleep_us, timeout_us);
> > +	clk_unprepare(clk);
> > +
> > +	return ret;
> > +}
> > +
> >  static inline int __must_check
> >  clk_bulk_prepare_enable(int num_clks, const struct clk_bulk_data
> > *clks)  {
> 
> --
> Kind regards,
> 
> Sakari Ailus

Patch

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index f5fa91a339d7..e10bb14c904d 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -13,6 +13,7 @@ 
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
 #include <linux/err.h>
+#include <linux/iopoll.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/of.h>
@@ -1160,6 +1161,34 @@  void clk_disable(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_disable);
 
+/**
+ * clk_poll_disabled - poll for clock gating.
+ * @clk: the clk that is going to stop
+ * @sleep_us: Maximum time to sleep between reads in us (0
+ *            tight-loops).  Should be less than ~20ms since usleep_range
+ *            is used (see Documentation/timers/timers-howto.rst).
+ * @timeout_us: Timeout in us, 0 means never timeout
+ *
+ * It polls for a clk to be stopped.
+ */
+int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64 timeout_us)
+{
+	bool status;
+
+	if (IS_ERR_OR_NULL(clk))
+		return 0;
+
+	if (!clk->core->ops->is_enabled)
+		return -EOPNOTSUPP;
+
+	if (WARN(__clk_get_enable_count(clk), "clk is in use\n"))
+		return -EBUSY;
+
+	return read_poll_timeout(__clk_is_enabled, status, !status, sleep_us,
+				 timeout_us, false, clk);
+}
+EXPORT_SYMBOL_GPL(clk_poll_disabled);
+
 static int clk_core_enable(struct clk_core *core)
 {
 	int ret = 0;
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 84b02518791f..7f714ecce0eb 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -693,6 +693,20 @@  int __must_check clk_bulk_enable(int num_clks,
  */
 void clk_disable(struct clk *clk);
 
+/**
+ * clk_poll_disabled - inform the system whether the clock source is stopped.
+ * @clk: clock source
+ * @sleep_us: Maximum time to sleep between reads in us (0
+ *            tight-loops).  Should be less than ~20ms since usleep_range
+ *            is used (see Documentation/timers/timers-howto.rst).
+ * @timeout_us: Timeout in us, 0 means never timeout
+ *
+ * Poll for clock gating and Inform the system about it's status.
+ *
+ * Context: May sleep.
+ */
+int clk_poll_disabled(struct clk *clk, unsigned long sleep_us, u64 timeout_us);
+
 /**
  * clk_bulk_disable - inform the system when the set of clks is no
  *		      longer required.
@@ -1030,6 +1044,11 @@  static inline int __must_check clk_bulk_enable(int num_clks,
 
 static inline void clk_disable(struct clk *clk) {}
 
+static inline int clk_poll_disabled(struct clk *clk, unsigned long sleep_us,
+				    u64 timeout_us)
+{
+	return 0;
+}
 
 static inline void clk_bulk_disable(int num_clks,
 				    const struct clk_bulk_data *clks) {}
@@ -1121,6 +1140,33 @@  static inline void clk_disable_unprepare(struct clk *clk)
 	clk_unprepare(clk);
 }
 
+/**
+ * clk_poll_disable_unprepare - Poll clk_disable_unprepare
+ * @clk: clock source
+ * @sleep_us: Maximum time to sleep between reads in us (0
+ *            tight-loops).  Should be less than ~20ms since usleep_range
+ *            is used (see Documentation/timers/timers-howto.rst).
+ * @timeout_us: Timeout in us, 0 means never timeout
+ *
+ * Context: May sleep.
+ *
+ * This function polls until the clock has stopped.
+ *
+ * Returns success (0) or negative errno.
+ */
+static inline int clk_poll_disable_unprepare(struct clk *clk,
+					     unsigned long sleep_us,
+					     u64 timeout_us)
+{
+	int ret;
+
+	clk_disable(clk);
+	ret = clk_poll_disabled(clk, sleep_us, timeout_us);
+	clk_unprepare(clk);
+
+	return ret;
+}
+
 static inline int __must_check
 clk_bulk_prepare_enable(int num_clks, const struct clk_bulk_data *clks)
 {