[RFC 4/7] clk: add support for clock protection

[mturquette@baylibre.com (Michael Turquette)]

Hi Jerome,

Quoting Jerome Brunet (2017-05-12 06:08:02)
> On Thu, 2017-05-11 at 12:05 -0700, Michael Turquette wrote:
> > Quoting Jerome Brunet (2017-03-21 11:33:27)
<snip>
> > > @@ -838,7 +933,9 @@ static int clk_core_determine_round(struct clk_core
> > > *core,
> > > ?{
> > > ????????long rate;
> > > ?
> > > -???????if (core->ops->determine_rate) {
> > > +???????if (clk_core_is_protected(core)) {
> > > +???????????????req->rate = core->rate;
> > 
> > Hmm, in CCF we basically re-use round_rate/determine_rate from within
> > calls to clk_set_rate. The point is that clk_set_rate should set the
> > same rate that is returned from either of the other two functions.
> > 
> > The change above breaks that subtle assumption, as a clk consumer can
> > now call:
> > 
> >       clk_protect(clk);
> > 
> >       rate = clk_get_rate(clk);               // rate is 1234;
> > 
> >       rate = clk_round_rate(clk, 5678);       // rate is STILL 1234
> > 
> >       ret = clk_set_rate(clk, 5678);
> > 
> >       rate = clk_get_rate(clk);               // rate is 5678
> > 
> > Is my understanding correct? If so then we might consider adding some
> > more complex knowledge to clk_round_rate. Something like:
> > 
> >       if clk_is_protected(clk) AND it is only protect by THIS clk:
> >               round the rate
> >       else:
> >               return core->rate
> 
> I may be wrong but I think it is already the way you want it. Please see below
> [0]
<snip>
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_unprotect(clk->core);
> > 
> > What happens here if two different users have both protected this same
> > clk? Looks like we ignore the second user?
> > 
> > In other words, what happens if clk->protect_ucount == 2?
> 
> We don't really care what is the value of the consumer count, what is important
> is whether it is null or not. This is linked to the point [0] above. Maybe it is
> not clear but here is how it (should) goes :
> 
> Every time clock_rate_protect is called the consumer *and* core count is
> incremented. (consumer_count =< core_count)
> 
> When an altering action is tried (set_rate, set_parent, ...), if the consumer
> count is not null, we call clk_core_unprotect which mean that the core_count is
> temporarily decremented by 1. It is safe to do so because we are holding the
> prepare_lock.
> 
> When we get to 
> +???????if (clk_core_is_protected(core)) {
> +???????????????req->rate = core->rate;
> 
> Either the clock was only protected by the calling consumer, *and only once*,
> then the protection has been temporarily removed, test is false and the usual
> code will be executed, calling round/determine rate.
> 
> If the test is true, it means the clock is still protected. This happens if 
> * the clock is protected and we come from an unprotected consumer
> * the clock is protected by more than one consumer
> * the clock is protected more than one time by the same consumer - when there is
> multiple code path protecting the rate in a device driver, as previously
> discussed. That's why clk_core_unprotect decrements by 1 and not by the
> consumer_count.
> 
> In such case, the clock is still protected, I think it make sense to return what
> is already set and not round/determine again. The clock was already
> rounded/determined when it wasn't protected.
> 
> It this what you meant by :
> > if clk_is_protected(clk) AND it is only protect by THIS clk:
> ?

Yes, you've answered my question and I'm happy with that. When reviewing
the code before I missed the subtle point that we test for
clk->protect_ucount but then only modify core->protect_count. I think a
one-line comment above those conditional statements would be nice.

I do have a doubt about how clk_round_rate works now. Is it correct that
we do not ever decrement the protect count when a protecting consumer
calls clk_round_rate?

It seems to me that a clk consumer should be able to call clk_protect()
and then clk_round_rate() and get a real rounded rate instead req->rate
= core->rate, assuming that the core protect count is decremented to
zero.

In other words, can you make clk_round_rate work like clk_set_rate and
clk_set_parent?

Regards,
Mike

> 
> Cheers
> Jerome
> 
> > 
> > 
> > Best regards,
> > Mike
> > 
> > > +
> > > ????????ret = clk_core_set_rate_nolock(clk->core, rate);
> > > ?
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_protect(clk->core);
> > > +
> > > ????????clk_prepare_unlock();
> > > ?
> > > ????????return ret;
> > > @@ -1669,12 +1772,18 @@ int clk_set_rate_range(struct clk *clk, unsigned
> > > long min, unsigned long max)
> > > ?
> > > ????????clk_prepare_lock();
> > > ?
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_unprotect(clk->core);
> > > +
> > > ????????if (min != clk->min_rate || max != clk->max_rate) {
> > > ????????????????clk->min_rate = min;
> > > ????????????????clk->max_rate = max;
> > > ????????????????ret = clk_core_set_rate_nolock(clk->core, clk->core-
> > > >req_rate);
> > > ????????}
> > > ?
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_protect(clk->core);
> > > +
> > > ????????clk_prepare_unlock();
> > > ?
> > > ????????return ret;
> > > @@ -1815,6 +1924,9 @@ static int clk_core_set_parent(struct clk_core *core,
> > > struct clk_core *parent)
> > > ????????if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count)
> > > ????????????????return -EBUSY;
> > > ?
> > > +???????if (clk_core_is_protected(core))
> > > +???????????????return -EBUSY;
> > > +
> > > ????????/* try finding the new parent index */
> > > ????????if (parent) {
> > > ????????????????p_index = clk_fetch_parent_index(core, parent);
> > > @@ -1878,11 +1990,24 @@ static int clk_core_set_parent_lock(struct clk_core
> > > *core,
> > > ? */
> > > ?int clk_set_parent(struct clk *clk, struct clk *parent)
> > > ?{
> > > +???????int ret;
> > > +
> > > ????????if (!clk)
> > > ????????????????return 0;
> > > ?
> > > -???????return clk_core_set_parent_lock(clk->core,
> > > -???????????????????????????????????????parent ? parent->core : NULL);
> > > +???????clk_prepare_lock();
> > > +
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_unprotect(clk->core);
> > > +
> > > +???????ret = clk_core_set_parent(clk->core, parent ? parent->core : NULL);
> > > +
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_protect(clk->core);
> > > +
> > > +???????clk_prepare_unlock();
> > > +
> > > +???????return ret;
> > > ?}
> > > ?EXPORT_SYMBOL_GPL(clk_set_parent);
> > > ?
> > > @@ -1893,7 +2018,10 @@ static int clk_core_set_phase(struct clk_core *core,
> > > int degrees)
> > > ????????if (!core)
> > > ????????????????return 0;
> > > ?
> > > -???????trace_clk_set_phase(clk->core, degrees);
> > > +???????if (clk_core_is_protected(core))
> > > +???????????????return -EBUSY;
> > > +
> > > +???????trace_clk_set_phase(core, degrees);
> > > ?
> > > ????????if (core->ops->set_phase)
> > > ????????????????ret = core->ops->set_phase(core->hw, degrees);
> > > @@ -1936,7 +2064,15 @@ int clk_set_phase(struct clk *clk, int degrees)
> > > ????????????????degrees += 360;
> > > ?
> > > ????????clk_prepare_lock();
> > > +
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_unprotect(clk->core);
> > > +
> > > ????????ret = clk_core_set_phase(clk->core, degrees);
> > > +
> > > +???????if (clk->protect_ucount)
> > > +???????????????clk_core_protect(clk->core);
> > > +
> > > ????????clk_prepare_unlock();
> > > ?
> > > ????????return ret;
> > > @@ -2023,11 +2159,12 @@ static void clk_summary_show_one(struct seq_file *s,
> > > struct clk_core *c,
> > > ????????if (!c)
> > > ????????????????return;
> > > ?
> > > -???????seq_printf(s, "%*s%-*s %11d %12d %11lu %10lu %-3d\n",
> > > +???????seq_printf(s, "%*s%-*s %11d %12d %12d %11lu %10lu %-3d\n",
> > > ???????????????????level * 3 + 1, "",
> > > ???????????????????30 - level * 3, c->name,
> > > -??????????????????c->enable_count, c->prepare_count, clk_core_get_rate(c),
> > > -??????????????????clk_core_get_accuracy(c), clk_core_get_phase(c));
> > > +??????????????????c->enable_count, c->prepare_count, c->protect_count,
> > > +??????????????????clk_core_get_rate(c), clk_core_get_accuracy(c),
> > > +??????????????????clk_core_get_phase(c));
> > > ?}
> > > ?
> > > ?static void clk_summary_show_subtree(struct seq_file *s, struct clk_core
> > > *c,
> > > @@ -2049,8 +2186,8 @@ static int clk_summary_show(struct seq_file *s, void
> > > *data)
> > > ????????struct clk_core *c;
> > > ????????struct hlist_head **lists = (struct hlist_head **)s->private;
> > > ?
> > > -???????seq_puts(s,
> > > "???clock?????????????????????????enable_cnt??prepare_cnt????????rate???accu
> > > racy???phase\n");
> > > -???????seq_puts(s, "-------------------------------------------------------
> > > ---------------------------------\n");
> > > +???????seq_puts(s,
> > > "???clock?????????????????????????enable_cnt??prepare_cnt??protect_cnt??????
> > > ??rate???accuracy???phase\n");
> > > +???????seq_puts(s, "-------------------------------------------------------
> > > ---------------------------------------------\n");
> > > ?
> > > ????????clk_prepare_lock();
> > > ?
> > > @@ -2085,6 +2222,7 @@ static void clk_dump_one(struct seq_file *s, struct
> > > clk_core *c, int level)
> > > ????????seq_printf(s, "\"%s\": { ", c->name);
> > > ????????seq_printf(s, "\"enable_count\": %d,", c->enable_count);
> > > ????????seq_printf(s, "\"prepare_count\": %d,", c->prepare_count);
> > > +???????seq_printf(s, "\"protect_count\": %d,", c->protect_count);
> > > ????????seq_printf(s, "\"rate\": %lu,", clk_core_get_rate(c));
> > > ????????seq_printf(s, "\"accuracy\": %lu,", clk_core_get_accuracy(c));
> > > ????????seq_printf(s, "\"phase\": %d", clk_core_get_phase(c));
> > > @@ -2191,6 +2329,11 @@ static int clk_debug_create_one(struct clk_core
> > > *core, struct dentry *pdentry)
> > > ????????if (!d)
> > > ????????????????goto err_out;
> > > ?
> > > +???????d = debugfs_create_u32("clk_protect_count", S_IRUGO, core->dentry,
> > > +???????????????????????(u32 *)&core->protect_count);
> > > +???????if (!d)
> > > +???????????????goto err_out;
> > > +
> > > ????????d = debugfs_create_u32("clk_notifier_count", S_IRUGO, core->dentry,
> > > ????????????????????????(u32 *)&core->notifier_count);
> > > ????????if (!d)
> > > @@ -2747,6 +2890,11 @@ void clk_unregister(struct clk *clk)
> > > ????????if (clk->core->prepare_count)
> > > ????????????????pr_warn("%s: unregistering prepared clock: %s\n",
> > > ????????????????????????????????????????__func__, clk->core->name);
> > > +
> > > +???????if (clk->core->protect_count)
> > > +???????????????pr_warn("%s: unregistering protected clock: %s\n",
> > > +???????????????????????????????????????__func__, clk->core->name);
> > > +
> > > ????????kref_put(&clk->core->ref, __clk_release);
> > > ?unlock:
> > > ????????clk_prepare_unlock();
> > > @@ -2905,6 +3053,15 @@ void __clk_put(struct clk *clk)
> > > ?
> > > ????????clk_prepare_lock();
> > > ?
> > > +???????/* Protect count not balanced: warn and sanitize */
> > > +???????if (clk->protect_ucount) {
> > > +???????????????pr_warn("%s: releasing protected clock: %s\n",
> > > +???????????????????????????????????????__func__, clk->core->name);
> > > +
> > > +???????????????for (; clk->protect_ucount; clk->protect_ucount--)
> > > +???????????????????????clk_core_unprotect(clk->core);
> > > +???????}
> > > +
> > > ????????hlist_del(&clk->clks_node);
> > > ????????if (clk->min_rate > clk->core->req_rate ||
> > > ????????????clk->max_rate < clk->core->req_rate)
> > > diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> > > index a428aec36ace..705a158d9b8f 100644
> > > --- a/include/linux/clk-provider.h
> > > +++ b/include/linux/clk-provider.h
> > > @@ -739,6 +739,7 @@ unsigned long clk_hw_get_rate(const struct clk_hw *hw);
> > > ?unsigned long __clk_get_flags(struct clk *clk);
> > > ?unsigned long clk_hw_get_flags(const struct clk_hw *hw);
> > > ?bool clk_hw_is_prepared(const struct clk_hw *hw);
> > > +bool clk_hw_is_protected(const struct clk_hw *hw);
> > > ?bool clk_hw_is_enabled(const struct clk_hw *hw);
> > > ?bool __clk_is_enabled(struct clk *clk);
> > > ?struct clk *__clk_lookup(const char *name);
> > > diff --git a/include/linux/clk.h b/include/linux/clk.h
> > > index e9d36b3e49de..90b72ead4411 100644
> > > --- a/include/linux/clk.h
> > > +++ b/include/linux/clk.h
> > > @@ -265,6 +265,30 @@ struct clk *devm_clk_get(struct device *dev, const char
> > > *id);
> > > ? */
> > > ?struct clk *devm_get_clk_from_child(struct device *dev,
> > > ????????????????????????????????????struct device_node *np, const char
> > > *con_id);
> > > +/**
> > > + * clk_protect - inform the system when the clock source should be
> > > protected.
> > > + * @clk: clock source
> > > + *
> > > + * This function informs the system that the consumer protecting the clock
> > > + * depends on the rate of the clock source and can't tolerate any glitches
> > > + * introduced by further clock rate change or re-parenting of the clock
> > > source.
> > > + *
> > > + * Must not be called from within atomic context.
> > > + */
> > > +void clk_protect(struct clk *clk);
> > > +
> > > +/**
> > > + * clk_unprotect - release the protection of the clock source.
> > > + * @clk: clock source
> > > + *
> > > + * This function informs the system that the consumer previously protecting
> > > the
> > > + * clock source can now deal with other consumer altering the clock source.
> > > + *
> > > + * The caller must balance the number of protect and unprotect calls.
> > > + *
> > > + * Must not be called from within atomic context.
> > > + */
> > > +void clk_unprotect(struct clk *clk);
> > > ?
> > > ?/**
> > > ? * clk_enable - inform the system when the clock source should be running.
> > > @@ -460,6 +484,11 @@ static inline void clk_put(struct clk *clk) {}
> > > ?
> > > ?static inline void devm_clk_put(struct device *dev, struct clk *clk) {}
> > > ?
> > > +
> > > +static inline void clk_protect(struct clk *clk) {}
> > > +
> > > +static inline void clk_unprotect(struct clk *clk) {}
> > > +
> > > ?static inline int clk_enable(struct clk *clk)
> > > ?{
> > > ????????return 0;
> > > --?
> > > 2.9.3
> > >