Hi Sakari Ailus,
Thanks for the feedback.
> -----Original Message-----
> From: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> Sent: Tuesday, February 27, 2024 9:36 AM
> Subject: Re: [PATCH v2 2/3] clk: Add clk_poll_disable_unprepare()
>
> Hi Biju,
>
> Thanks for the patchset.
>
> On Tue, Feb 20, 2024 at 10:43:35AM +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 <biju.das.jz@xxxxxxxxxxxxxx>
> > ---
> > 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 | 23 +++++++++++++++++++++++
> > include/linux/clk.h | 46
> > +++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 69 insertions(+)
> >
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index
> > 9a09f51f4af1..0e66b7180388 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>
> > @@ -1138,6 +1139,28 @@ 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;
> > +
> > + return read_poll_timeout(__clk_is_enabled, status, !status, sleep_us,
> > + timeout_us, false, clk);
>
> This API is a bit problematic as anything else in the system could enable or disable the clock while
> polling happens. I think you should add a warning that this may only be used if the user is the sole
> user of the clock in the system (which is of course hard to guarantee in a general
> case) and has not increased the enable count (or has decremented it again to zero).
Agreed.
>
> I'd perhaps go as far as do WARN_ON(enable count non-zero) and return an error code (-EBUSY).
OK, the below code should cover the above case and below one right?
+ if (!clk->core->ops->is_enabled)
+ return -EOPNOTSUPP;
+
+ if (WARN(__clk_get_enable_count(clk), "clk is in use\n"))
+ return -EBUSY;
+
>
> > +}
> > +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
> > e6acec5d8dbe..2d63a12214e5 100644
> > --- a/include/linux/clk.h
> > +++ b/include/linux/clk.h
> > @@ -665,6 +665,20 @@ 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.
> > @@ -996,6 +1010,11 @@ 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) {} @@ -1087,6 +1106,33 @@
> > 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);
>
> How about clocks that are generated by devices to which access always sleeps, such as I²C devices? I
> presume they're actually stopped in
> clk_unprepare() as clk_disable() may not sleep. They also can't implement is_enabled as it cannot
> sleep either.
>
> It seems to depend on the implementation on what they do. The runtime PM function used is
> pm_runtime_put_sync(), so you may have a guarantee the device is powered off but ONLY if it had no
> other users and had runtime PM enabled.
Even in RPM case, at the end, it comes down to enable count. So, the check you mentioned
for enabled_could should be fine??
>
> So perhaps return an error if there's no is_enabled() callback?
OK, This will be taken care inside clk_poll_disabled().
Cheers,
Biju
>
> > +
> > + return ret;
> > +}
> > +
> > static inline int __must_check
> > clk_bulk_prepare_enable(int num_clks, const struct clk_bulk_data
> > *clks) {
>
