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Date: Thu, 30 Apr 2015 08:08:06 +0200
From: Sascha Hauer <s.hauer@...gutronix.de>
To: linux-clk@...r.kernel.org
Cc: Michael Turquette <mturquette@...aro.org>, kernel@...gutronix.de,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Lee Jones <lee.jones@...aro.org>,
Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: [RFC] clk: introduce critical clocks
Some clocks are so critical to the system that they must never be turned
off unless explicitly requested. Normally unused clocks get disabled in
the clk_disable_unused initcall. Currently there are two ways for
keeping clocks enabled even if they are unused, both with their own
drawbacks:
- The CLK_IGNORE_UNUSED flag. Clocks with this flags are not disabled
during clk_disable_unused. The problem with this is that these clocks
are skipped during the clk_disable_unused initcall, but can get
disabled due to normal clk_enable/disable at any time, not necessarily
even on operations on the critical clocks themselves but on operations
on their ancestors, siblings or children.
- call clk_prepare_enable right after registration in the clock
driver. This works properly, but due to the increased enable counter
the clock will never get disabled, even not when a proper user
comes along who knows when the clock can safely be disabled.
This patch solves this by introducing two new API calls:
clk_prepare_enable_critical() will call clk_prepare_enable() on a clock
and additionally set a 'critical' flag on the clock. This call is
intended for clock providers which provide a critical clock.
clk_disable_unprepare_critical() is intended for consumers of a critical
clock. Consumers should first call clk_prepare_enable() on a clock to
get their own prepare/enable reference and call
clk_disable_unprepare_critical() afterwards. This will clear the
'critical' flag from the clock and decrease the prepare/enable counter.
The ownership of the clock is now transferred to the consumer. Calling
clk_disable_unprepare_critical() on a clock which doesn't have the
'critical' flag set is just a no-op, so consumers can safely call this
on their clocks.
To make this more versatile a clk flag could be introduced which could
be set during registration so that clk providers would not have to make
this API call on each critical clock. I haven't implemented this yet
because it turned out not to be trivial. clk_prepare_enable can only
be called when the clock is not orphaned which may not be the case
during registration time. I can implement this if this way of handling
critical clocks is considered suitable for mainline.
Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
---
drivers/clk/clk.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/clk-provider.h | 2 ++
include/linux/clk.h | 10 ++++++++++
3 files changed, 58 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 459ce9d..d57d4fd 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -64,6 +64,7 @@ struct clk_core {
unsigned long flags;
unsigned int enable_count;
unsigned int prepare_count;
+ bool enable_critical;
unsigned long accuracy;
int phase;
struct hlist_head children;
@@ -940,7 +941,13 @@ void clk_unprepare(struct clk *clk)
return;
clk_prepare_lock();
+
+ if (clk->core->enable_critical)
+ goto out;
+
clk_core_unprepare(clk->core);
+
+out:
clk_prepare_unlock();
}
EXPORT_SYMBOL_GPL(clk_unprepare);
@@ -995,7 +1002,9 @@ int clk_prepare(struct clk *clk)
return 0;
clk_prepare_lock();
+
ret = clk_core_prepare(clk->core);
+
clk_prepare_unlock();
return ret;
@@ -2250,6 +2259,43 @@ bool clk_is_match(const struct clk *p, const struct clk *q)
}
EXPORT_SYMBOL_GPL(clk_is_match);
+int clk_prepare_enable_critical(struct clk *clk)
+{
+ if (!clk)
+ return 0;
+
+ clk_prepare_lock();
+ if (clk->core->enable_critical) {
+ clk_prepare_unlock();
+ return -EBUSY;
+ }
+
+ clk->core->enable_critical = true;
+
+ clk_prepare_unlock();
+
+ return clk_prepare_enable(clk);
+
+}
+
+void clk_disable_unprepare_critical(struct clk *clk)
+{
+ if (!clk)
+ return;
+
+ clk_prepare_lock();
+ if (!clk->core->enable_critical) {
+ clk_prepare_unlock();
+ return;
+ }
+
+ clk->core->enable_critical = false;
+
+ clk_prepare_unlock();
+
+ clk_disable_unprepare(clk);
+}
+
/**
* __clk_init - initialize the data structures in a struct clk
* @dev: device initializing this clk, placeholder for now
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index df69531..8727c12 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -694,5 +694,7 @@ struct dentry *clk_debugfs_add_file(struct clk_hw *hw, char *name, umode_t mode,
void *data, const struct file_operations *fops);
#endif
+int clk_prepare_enable_critical(struct clk *clk);
+
#endif /* CONFIG_COMMON_CLK */
#endif /* CLK_PROVIDER_H */
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 68c16a6..b259e36 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -138,6 +138,16 @@ int clk_get_phase(struct clk *clk);
*/
bool clk_is_match(const struct clk *p, const struct clk *q);
+/**
+ * clk_disable_unprepare_critical - remove critical flag from clock
+ * @clk: clock source
+ *
+ * This removes the critical flag from a clock and disables it. The
+ * consumer should have enabled the clock by itself now if it wants
+ * to keep the clock enabled.
+ */
+void clk_disable_unprepare_critical(struct clk *clk);
+
#else
static inline long clk_get_accuracy(struct clk *clk)
--
2.1.4
--
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