[PATCH v2 05/11] clk: add support for clock protection
Jerome Brunet
jbrunet at baylibre.com
Mon May 29 02:15:09 PDT 2017
On Thu, 2017-05-25 at 13:58 -0700, Michael Turquette wrote:
> Quoting Jerome Brunet (2017-05-21 14:59:52)
> > The patch adds clk_protect and clk_unprotect to the CCF API. These
> > functions allow a consumer to inform the system that the rate of clock is
> > critical to for its operations and it can't tolerate other consumers
> > changing the rate or introducing glitches while the clock is protected.
> >
> > Signed-off-by: Jerome Brunet <jbrunet at baylibre.com>
> > ---
> > drivers/clk/clk.c | 207
> > +++++++++++++++++++++++++++++++++++++++++--
> > include/linux/clk-provider.h | 1 +
> > include/linux/clk.h | 29 ++++++
> > 3 files changed, 230 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index 1a8c0d013238..a0524e3bfaca 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -60,6 +60,7 @@ struct clk_core {
> > bool orphan;
> > unsigned int enable_count;
> > unsigned int prepare_count;
> > + unsigned int protect_count;
> > unsigned long min_rate;
> > unsigned long max_rate;
> > unsigned long accuracy;
> > @@ -84,6 +85,7 @@ struct clk {
> > const char *con_id;
> > unsigned long min_rate;
> > unsigned long max_rate;
> > + unsigned long protect_count;
> > struct hlist_node clks_node;
> > };
> >
> > @@ -160,6 +162,11 @@ static bool clk_core_is_prepared(struct clk_core *core)
> > return core->ops->is_prepared(core->hw);
> > }
> >
> > +static bool clk_core_rate_is_protected(struct clk_core *core)
> > +{
> > + return core->protect_count;
> > +}
> > +
> > static bool clk_core_is_enabled(struct clk_core *core)
> > {
> > /*
> > @@ -328,6 +335,11 @@ bool clk_hw_is_prepared(const struct clk_hw *hw)
> > return clk_core_is_prepared(hw->core);
> > }
> >
> > +bool clk_hw_rate_is_protected(const struct clk_hw *hw)
> > +{
> > + return clk_core_rate_is_protected(hw->core);
> > +}
> > +
> > bool clk_hw_is_enabled(const struct clk_hw *hw)
> > {
> > return clk_core_is_enabled(hw->core);
> > @@ -584,6 +596,102 @@ int clk_prepare(struct clk *clk)
> > }
> > EXPORT_SYMBOL_GPL(clk_prepare);
> >
> > +static void clk_core_rate_unprotect(struct clk_core *core)
> > +{
> > + lockdep_assert_held(&prepare_lock);
> > +
> > + if (!core)
> > + return;
> > +
> > + if (WARN_ON(core->protect_count == 0))
> > + return;
> > +
> > + if (--core->protect_count > 0)
> > + return;
> > +
> > + clk_core_rate_unprotect(core->parent);
> > +}
> > +
> > +/**
> > + * clk_rate_unprotect - unprotect the rate of a clock source
> > + * @clk: the clk being unprotected
> > + *
> > + * clk_unprotect completes a critical section during which the clock
> > + * consumer cannot tolerate any change to the clock rate. If no other clock
> > + * consumers have protected clocks in the parent chain, then calls to this
> > + * function will allow the clocks in the parent chain to change rates
> > + * freely.
> > + *
> > + * Unlike the clk_set_rate_range method, which allows the rate to change
> > + * within a given range, protected clocks cannot have their rate changed,
> > + * either directly or indirectly due to changes further up the parent chain
> > + * of clocks.
> > + *
> > + * Calls to clk_unprotect must be balanced with calls to clk_protect. Calls
> > + * to this function may sleep, and do not return error status.
> > + */
> > +void clk_rate_unprotect(struct clk *clk)
> > +{
> > + if (!clk)
> > + return;
> > +
> > + clk_prepare_lock();
> > +
> > + /*
> > + * if there is something wrong with this consumer protect count,
> > stop
> > + * here before messing with the provider
> > + */
> > + if (WARN_ON(clk->protect_count <= 0))
> > + goto out;
> > +
> > + clk_core_rate_unprotect(clk->core);
> > + clk->protect_count--;
> > +out:
> > + clk_prepare_unlock();
> > +}
> > +EXPORT_SYMBOL_GPL(clk_rate_unprotect);
> > +
> > +static void clk_core_rate_protect(struct clk_core *core)
> > +{
> > + lockdep_assert_held(&prepare_lock);
> > +
> > + if (!core)
> > + return;
> > +
> > + if (core->protect_count == 0)
> > + clk_core_rate_protect(core->parent);
> > +
> > + core->protect_count++;
> > +}
> > +
> > +/**
> > + * clk_rate_protect - protect a clock source
> > + * @clk: the clk being protected
> > + *
> > + * clk_protect begins a critical section during which the clock consumer
> > + * cannot tolerate any change to the clock rate. This results in all clocks
> > + * up the parent chain to also be rate-protected.
> > + *
> > + * Unlike the clk_set_rate_range method, which allows the rate to change
> > + * within a given range, protected clocks cannot have their rate changed,
> > + * either directly or indirectly due to changes further up the parent chain
> > + * of clocks.
> > + *
> > + * Calls to clk_protect should be balanced with calls to clk_unprotect.
> > + * Calls to this function may sleep, and do not return error status.
> > + */
> > +void clk_rate_protect(struct clk *clk)
> > +{
> > + if (!clk)
> > + return;
> > +
> > + clk_prepare_lock();
> > + clk_core_rate_protect(clk->core);
> > + clk->protect_count++;
> > + clk_prepare_unlock();
> > +}
> > +EXPORT_SYMBOL_GPL(clk_rate_protect);
> > +
> > static void clk_core_disable(struct clk_core *core)
> > {
> > lockdep_assert_held(&enable_lock);
> > @@ -838,7 +946,15 @@ static int clk_core_determine_round(struct clk_core
> > *core,
> > {
> > long rate;
> >
> > - if (core->ops->determine_rate) {
> > + /*
> > + * At this point, core protection will be disabled if
> > + * - if the provider is not protected at all
> > + * - if the calling consumer is the only one protecting the
> > + * provider (and only once)
> > + */
> > + if (clk_core_rate_is_protected(core)) {
> > + req->rate = core->rate;
> > + } else if (core->ops->determine_rate) {
> > return core->ops->determine_rate(core->hw, req);
> > } else if (core->ops->round_rate) {
> > rate = core->ops->round_rate(core->hw, req->rate,
> > @@ -944,10 +1060,17 @@ long clk_round_rate(struct clk *clk, unsigned long
> > rate)
> >
> > clk_prepare_lock();
> >
> > + if (clk->protect_count)
> > + clk_core_rate_unprotect(clk->core);
> > +
> > clk_core_get_boundaries(clk->core, &req.min_rate, &req.max_rate);
> > req.rate = rate;
> >
> > ret = clk_core_round_rate_nolock(clk->core, &req);
> > +
> > + if (clk->protect_count)
> > + clk_core_rate_protect(clk->core);
> > +
> > clk_prepare_unlock();
> >
> > if (ret)
> > @@ -1575,15 +1698,24 @@ static unsigned long
> > clk_core_req_round_rate_nolock(struct clk_core *core,
>
> There are way too many round_rate and determine_rate functions.
>
> Here is a list of round_rate and determine_rate "helpers":
>
> static int clk_core_determine_round(struct clk_core *core,
> struct clk_rate_request *req)
> (called by clk_core_round_rate_nolock and clk_calc_new_rates)
>
> static int clk_core_round_rate_nolock(struct clk_core *core,
> struct clk_rate_request *req)
> (called in several places)
>
> int __clk_determine_rate(struct clk_hw *hw, struct clk_rate_request *req)
> (called by a few provider drivers. Should probably be renamed as I
> mentioned in my previous response)
>
> unsigned long clk_hw_round_rate(struct clk_hw *hw, unsigned long rate)
> (used a whole lot)
>
> static unsigned long clk_core_req_round_rate_nolock(struct clk_core *core,
> unsigned long req_rate)
> (only called by clk_core_set_rate_nolock. Can we replace with one of the
> options above? Probably clk_core_round_rate_nolock)
Agreed, we could clean this a bit I suppose
>
> > {
> > int ret;
> > struct clk_rate_request req;
> > + unsigned int cnt = core->protect_count;
> >
> > if (!core)
> > return 0;
> >
> > + /* simulate what the rate would be if it could be freely set */
> > + while (core->protect_count)
> > + clk_core_rate_unprotect(core);
>
> Gross. Why do this here and not in similar functions like
> clk_core_round_rate_nolock?
I agree it isn't very nice but there is a good reason for this.
When a provider is protected, all you are going to get from round_rate is the
current rate - which is the expected result.
At this point, we are trying to figure out if the request of the consumer would
require the provider to change its settings, whether it is protected or not.
In order to get that, we need to unroll the protection applied to this provider
along the tree. This why I needed a specific helper, otherwise there is no
reason to unroll the protection.
If parent providers are still protected by siblings after that, it is a
constraints on the clock tree and it is fine.
>
> > +
> > clk_core_get_boundaries(core, &req.min_rate, &req.max_rate);
> > req.rate = req_rate;
> >
> > ret = clk_core_round_rate_nolock(core, &req);
> >
> > + /* restore the protection */
> > + while (core->protect_count < cnt)
> > + clk_core_rate_protect(core);
> > +
> > return ret ? 0 : req.rate;
> > }
> >
> > @@ -1602,6 +1734,10 @@ static int clk_core_set_rate_nolock(struct clk_core
> > *core,
> > if (rate == clk_core_get_rate_nolock(core))
> > return 0;
> >
> > + /* fail on a direct rate set of a protected provider */
> > + if (clk_core_rate_is_protected(core))
> > + return -EBUSY;
>
> Again, why bother unrolling the protected clocks in
> clk_core_req_round_rate_nolock if any protection will cause the
> operation to fail here?
If we don't unroll the protection on a protected clock:
(round_rate(requested_rate) == clk_core_get_rate_nolock(core)) would always be
true and we would never get to this check.
We should get to this point only if the request requires a change of the
settings. If the clock is protected, we should tell the consumer its request
can't be (optimally) satisfied.
All this sounds like obscur corner case but I think it may happen more often
than we think:
Imagine the 2 consumers requesting the same rate from a provider (ex: 48000) and
the provider only approximately match it (ex 48010):
1 - Consumer #1 request 48000
2 - Rate is set to 48010 and set rate successfully returns
3 - Consumer #2 request 48000 as well
-> Should it get different result than consumer #1 ?
As it is, requested rate is different from the rate set and set_rate reports
-EBUSY
With the proposed change, set_rate is able to figure out that we are already on
the best setting and report success to the consumer. From the consumer point of
view, I think this is more coherent.
>
> Best regards,
> Mike
>
> > +
> > if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
> > return -EBUSY;
> >
> > @@ -1658,8 +1794,14 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
> > /* prevent racing with updates to the clock topology */
> > clk_prepare_lock();
> >
> > + if (clk->protect_count)
> > + clk_core_rate_unprotect(clk->core);
> > +
> > ret = clk_core_set_rate_nolock(clk->core, rate);
> >
> > + if (clk->protect_count)
> > + clk_core_rate_protect(clk->core);
> > +
> > clk_prepare_unlock();
> >
> > return ret;
> > @@ -1690,12 +1832,18 @@ int clk_set_rate_range(struct clk *clk, unsigned
> > long min, unsigned long max)
> >
> > clk_prepare_lock();
> >
> > + if (clk->protect_count)
> > + clk_core_rate_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_count)
> > + clk_core_rate_protect(clk->core);
> > +
> > clk_prepare_unlock();
> >
> > return ret;
> > @@ -1837,6 +1985,9 @@ static int clk_core_set_parent_nolock(struct clk_core
> > *core,
> > if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count)
> > return -EBUSY;
> >
> > + if (clk_core_rate_is_protected(core))
> > + return -EBUSY;
> > +
> > /* try finding the new parent index */
> > if (parent) {
> > p_index = clk_fetch_parent_index(core, parent);
> > @@ -1894,8 +2045,16 @@ int clk_set_parent(struct clk *clk, struct clk
> > *parent)
> > return 0;
> >
> > clk_prepare_lock();
> > +
> > + if (clk->protect_count)
> > + clk_core_rate_unprotect(clk->core);
> > +
> > ret = clk_core_set_parent_nolock(clk->core,
> > parent ? parent->core : NULL);
> > +
> > + if (clk->protect_count)
> > + clk_core_rate_protect(clk->core);
> > +
> > clk_prepare_unlock();
> >
> > return ret;
> > @@ -1909,7 +2068,10 @@ static int clk_core_set_phase_nolock(struct clk_core
> > *core, int degrees)
> > if (!core)
> > return 0;
> >
> > - trace_clk_set_phase(clk->core, degrees);
> > + if (clk_core_rate_is_protected(core))
> > + return -EBUSY;
> > +
> > + trace_clk_set_phase(core, degrees);
> >
> > if (core->ops->set_phase)
> > ret = core->ops->set_phase(core->hw, degrees);
> > @@ -1952,7 +2114,15 @@ int clk_set_phase(struct clk *clk, int degrees)
> > degrees += 360;
> >
> > clk_prepare_lock();
> > +
> > + if (clk->protect_count)
> > + clk_core_rate_unprotect(clk->core);
> > +
> > ret = clk_core_set_phase_nolock(clk->core, degrees);
> > +
> > + if (clk->protect_count)
> > + clk_core_rate_protect(clk->core);
> > +
> > clk_prepare_unlock();
> >
> > return ret;
> > @@ -2039,11 +2209,12 @@ 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,
> > @@ -2065,8 +2236,8 @@ 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();
> >
> > @@ -2101,6 +2272,7 @@ 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));
> > @@ -2231,6 +2403,11 @@ 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)
> > @@ -2794,6 +2971,11 @@ 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();
> > @@ -2952,6 +3134,17 @@ void __clk_put(struct clk *clk)
> >
> > clk_prepare_lock();
> >
> > + /*
> > + * Before calling clk_put, all calls to clk_rate_protect from a
> > given
> > + * user must be balanced with calls to clk_rate_unprotect and by
> > that
> > + * same user
> > + */
> > + WARN_ON(clk->protect_count);
> > +
> > + /* We voiced our concern, let's sanitize the situation */
> > + for (; clk->protect_count; clk->protect_count--)
> > + clk_core_rate_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..ebd7df5f375f 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_rate_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 024cd07870d0..85d73e02df40 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_rate_protect - inform the system when the clock rate must 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_rate_protect(struct clk *clk);
> > +
> > +/**
> > + * clk_rate_unprotect - release the protection of the clock source.
> > + * @clk: clock source
> > + *
> > + * This function informs the system that the consumer previously protecting
> > the
> > + * clock rate can now deal with other consumer altering the clock source
> > rate
> > + *
> > + * The caller must balance the number of rate_protect and rate_unprotect
> > calls.
> > + *
> > + * Must not be called from within atomic context.
> > + */
> > +void clk_rate_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;
> > --
> > 2.9.4
> >
> > --
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