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* [RFC PATCH 1/2] clk: add clk accuracy retrieval support
@ 2013-08-01 15:02 Boris BREZILLON
  2013-08-01 15:06 ` boris brezillon
  0 siblings, 1 reply; 3+ messages in thread
From: Boris BREZILLON @ 2013-08-01 15:02 UTC (permalink / raw)
  To: Mike Turquette, Russell King, Rob Landley
  Cc: linux-kernel, linux-arm-kernel, linux-doc, Boris BREZILLON

The clock accuracy is expressed in ppb (parts per billion) and represents
the possible clock drift.
Say you have a clock (e.g. an oscillator) which provides a fixed clock of
20MHz with an accuracy of +- 20Hz. This accuracy expressed in ppb is
20Hz/20MHz = 1000 ppb (or 1 ppm).

Clock users may need the clock accuracy information in order to choose
the best clock (the one with the best accuracy) across several available
clocks.

This patch adds clk accuracy retrieval support for common clk framework by
means of a new function called clk_get_accuracy.
This function returns the given clock accuracy expressed in ppb.

In order to get the clock accuracy, this implementation adds one callback
called recalc_accuracy to the clk_ops structure.
This callback is given the parent clock accuracy (if the clock is not a
root clock) and should recalculate the given clock accuracy.

This callback is optional and may be implemented if the clock is not
a perfect clock (accuracy != 0 ppb).

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
---
 Documentation/clk.txt        |    4 ++
 drivers/clk/Kconfig          |    4 ++
 drivers/clk/clk.c            |   91 ++++++++++++++++++++++++++++++++++++++++--
 include/linux/clk-private.h  |    1 +
 include/linux/clk-provider.h |   11 +++++
 include/linux/clk.h          |   17 ++++++++
 6 files changed, 124 insertions(+), 4 deletions(-)

diff --git a/Documentation/clk.txt b/Documentation/clk.txt
index 6f68ba0..869a4a3 100644
--- a/Documentation/clk.txt
+++ b/Documentation/clk.txt
@@ -73,6 +73,8 @@ the operations defined in clk.h:
 		int		(*set_parent)(struct clk_hw *hw, u8 index);
 		u8		(*get_parent)(struct clk_hw *hw);
 		int		(*set_rate)(struct clk_hw *hw, unsigned long);
+		unsigned long	(*recalc_accuracy)(struct clk_hw *hw,
+						   unsigned long parent_accuracy);
 		void		(*init)(struct clk_hw *hw);
 	};
 
@@ -197,6 +199,8 @@ optional or must be evaluated on a case-by-case basis.
 .set_parent  |      |             | n             | y           | n    |
 .get_parent  |      |             | n             | y           | n    |
              |      |             |               |             |      |
+.recalc_rate |      |             |               |             |      |
+             |      |             |               |             |      |
 .init        |      |             |               |             |      |
 	     -----------------------------------------------------------
 
diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 51380d6..205a19b 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -6,12 +6,16 @@ config CLKDEV_LOOKUP
 config HAVE_CLK_PREPARE
 	bool
 
+config HAVE_CLK_GET_ACCURACY
+	bool
+
 config HAVE_MACH_CLKDEV
 	bool
 
 config COMMON_CLK
 	bool
 	select HAVE_CLK_PREPARE
+	select HAVE_CLK_GET_ACCURACY
 	select CLKDEV_LOOKUP
 	---help---
 	  The common clock framework is a single definition of struct
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 54a191c..f8e68ca 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -104,10 +104,11 @@ static void clk_summary_show_one(struct seq_file *s, struct clk *c, int level)
 	if (!c)
 		return;
 
-	seq_printf(s, "%*s%-*s %-11d %-12d %-10lu",
+	seq_printf(s, "%*s%-*s %-11d %-12d %-10lu %-11lu",
 		   level * 3 + 1, "",
 		   30 - level * 3, c->name,
-		   c->enable_count, c->prepare_count, clk_get_rate(c));
+		   c->enable_count, c->prepare_count, clk_get_rate(c),
+		   clk_get_accuracy(c));
 	seq_printf(s, "\n");
 }
 
@@ -129,8 +130,8 @@ static int clk_summary_show(struct seq_file *s, void *data)
 {
 	struct clk *c;
 
-	seq_printf(s, "   clock                        enable_cnt  prepare_cnt  rate\n");
-	seq_printf(s, "---------------------------------------------------------------------\n");
+	seq_printf(s, "   clock                        enable_cnt  prepare_cnt  rate        accuracy\n");
+	seq_printf(s, "---------------------------------------------------------------------------------\n");
 
 	clk_prepare_lock();
 
@@ -167,6 +168,7 @@ static void clk_dump_one(struct seq_file *s, struct clk *c, int level)
 	seq_printf(s, "\"enable_count\": %d,", c->enable_count);
 	seq_printf(s, "\"prepare_count\": %d,", c->prepare_count);
 	seq_printf(s, "\"rate\": %lu", clk_get_rate(c));
+	seq_printf(s, "\"accuracy\": %lu", clk_get_accuracy(c));
 }
 
 static void clk_dump_subtree(struct seq_file *s, struct clk *c, int level)
@@ -248,6 +250,11 @@ static int clk_debug_create_one(struct clk *clk, struct dentry *pdentry)
 	if (!d)
 		goto err_out;
 
+	d = debugfs_create_u32("clk_accuracy", S_IRUGO, clk->dentry,
+			(u32 *)&clk->accuracy);
+	if (!d)
+		goto err_out;
+
 	d = debugfs_create_x32("clk_flags", S_IRUGO, clk->dentry,
 			(u32 *)&clk->flags);
 	if (!d)
@@ -590,6 +597,11 @@ out:
 	return ret;
 }
 
+unsigned long __clk_get_accuracy(struct clk *clk)
+{
+	return !clk ? 0 : clk->accuracy;
+}
+
 unsigned long __clk_get_flags(struct clk *clk)
 {
 	return !clk ? 0 : clk->flags;
@@ -950,6 +962,58 @@ static int __clk_notify(struct clk *clk, unsigned long msg,
 }
 
 /**
+ * __clk_recalc_accuracies
+ * @clk: first clk in the subtree
+ * @msg: notification type (see include/linux/clk.h)
+ *
+ * Walks the subtree of clks starting with clk and recalculates accuracies as
+ * it goes.  Note that if a clk does not implement the .recalc_rate callback
+ * then it is assumed that the clock will take on the rate of it's parent.
+ *
+ * Caller must hold prepare_lock.
+ */
+static void __clk_recalc_accuracies(struct clk *clk)
+{
+	unsigned long parent_accuracy = 0;
+	struct clk *child;
+
+	if (clk->parent)
+		parent_accuracy = clk->parent->accuracy;
+
+	if (clk->ops->recalc_accuracy)
+		clk->accuracy = clk->ops->recalc_accuracy(clk->hw, parent_accuracy);
+	else
+		clk->accuracy = parent_accuracy;
+
+	hlist_for_each_entry(child, &clk->children, child_node)
+		__clk_recalc_accuracies(child);
+}
+
+/**
+ * clk_get_accuracy - return the accuracy of clk
+ * @clk: the clk whose accuracy is being returned
+ *
+ * Simply returns the cached accuracy of the clk, unless
+ * CLK_GET_ACCURACY_NOCACHE flag is set, which means a recalc_rate will be
+ * issued.
+ * If clk is NULL then returns 0.
+ */
+unsigned long clk_get_accuracy(struct clk *clk)
+{
+	unsigned long accuracy;
+	clk_prepare_lock();
+
+	if (clk && (clk->flags & CLK_GET_ACCURACY_NOCACHE))
+		__clk_recalc_accuracies(clk);
+
+	accuracy = __clk_get_accuracy(clk);
+	clk_prepare_unlock();
+
+	return accuracy;
+}
+EXPORT_SYMBOL_GPL(clk_get_accuracy);
+
+/**
  * __clk_recalc_rates
  * @clk: first clk in the subtree
  * @msg: notification type (see include/linux/clk.h)
@@ -1343,6 +1407,7 @@ void __clk_reparent(struct clk *clk, struct clk *new_parent)
 {
 	clk_reparent(clk, new_parent);
 	clk_debug_reparent(clk, new_parent);
+	__clk_recalc_accuracies(clk);
 	__clk_recalc_rates(clk, POST_RATE_CHANGE);
 }
 
@@ -1502,6 +1567,9 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 	/* do the re-parent */
 	ret = __clk_set_parent(clk, parent, p_index);
 
+	/* propagate accuracy recalculation */
+	__clk_recalc_accuracies(clk);
+
 	/* propagate rate recalculation accordingly */
 	if (ret)
 		__clk_recalc_rates(clk, ABORT_RATE_CHANGE);
@@ -1610,6 +1678,21 @@ int __clk_init(struct device *dev, struct clk *clk)
 		hlist_add_head(&clk->child_node, &clk_orphan_list);
 
 	/*
+	 * Set clk's accuracy.  The preferred method is to use
+	 * .recalc_accuracy. For simple clocks and lazy developers the default
+	 * fallback is to use the parent's accuracy.  If a clock doesn't have a
+	 * parent (or is orphaned) then accuracy is set to zero (perfect
+	 * clock).
+	 */
+	if (clk->ops->recalc_accuracy)
+		clk->accuracy = clk->ops->recalc_accuracy(clk->hw,
+					__clk_get_accuracy(clk->parent));
+	else if (clk->parent)
+		clk->accuracy = clk->parent->accuracy;
+	else
+		clk->accuracy = 0;
+
+	/*
 	 * Set clk's rate.  The preferred method is to use .recalc_rate.  For
 	 * simple clocks and lazy developers the default fallback is to use the
 	 * parent's rate.  If a clock doesn't have a parent (or is orphaned)
diff --git a/include/linux/clk-private.h b/include/linux/clk-private.h
index dd7adff..dbbd0cf 100644
--- a/include/linux/clk-private.h
+++ b/include/linux/clk-private.h
@@ -38,6 +38,7 @@ struct clk {
 	unsigned long		flags;
 	unsigned int		enable_count;
 	unsigned int		prepare_count;
+	unsigned long		accuracy;
 	struct hlist_head	children;
 	struct hlist_node	child_node;
 	unsigned int		notifier_count;
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 1ec14a7..2127fbc 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -27,6 +27,7 @@
 #define CLK_IS_ROOT		BIT(4) /* root clk, has no parent */
 #define CLK_IS_BASIC		BIT(5) /* Basic clk, can't do a to_clk_foo() */
 #define CLK_GET_RATE_NOCACHE	BIT(6) /* do not use the cached clk rate */
+#define CLK_GET_ACCURACY_NOCACHE	BIT(7) /* do not use the cached clk accuracy */
 
 struct clk_hw;
 
@@ -102,6 +103,13 @@ struct clk_hw;
  *		which is likely helpful for most .set_rate implementation.
  *		Returns 0 on success, -EERROR otherwise.
  *
+ * @recalc_accuracy: Recalculate the accuracy of this clock. The clock accuracy
+ * 		is expressed in ppb (parts per billion). The parent accuracy is
+ * 		an input parameter.
+ * 		Returns the calculated accuracy.  Optional - if	this op is not
+ * 		set then clock accuracy will be initialized to parent accuracy
+ * 		or 0 (perfect clock) if clock has no parent.
+ *
  * The clk_enable/clk_disable and clk_prepare/clk_unprepare pairs allow
  * implementations to split any work between atomic (enable) and sleepable
  * (prepare) contexts.  If enabling a clock requires code that might sleep,
@@ -130,6 +138,8 @@ struct clk_ops {
 	u8		(*get_parent)(struct clk_hw *hw);
 	int		(*set_rate)(struct clk_hw *hw, unsigned long,
 				    unsigned long);
+	unsigned long	(*recalc_accuracy)(struct clk_hw *hw,
+					   unsigned long parent_accuracy);
 	void		(*init)(struct clk_hw *hw);
 };
 
@@ -185,6 +195,7 @@ struct clk_hw {
 struct clk_fixed_rate {
 	struct		clk_hw hw;
 	unsigned long	fixed_rate;
+	unsigned long	fixed_accuracy;
 	u8		flags;
 };
 
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 9a6d045..44fd65a 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -85,6 +85,23 @@ int clk_notifier_unregister(struct clk *clk, struct notifier_block *nb);
 #endif
 
 /**
+ * clk_get_accuracy - obtain the clock accuracy in ppb (parts per billion)
+ * 		      for a clock source.
+ * @clk: clock source
+ *
+ * This gets the clock source accuracy expressed in ppb.
+ * A perfect clock returns 0.
+ */
+#ifdef CONFIG_HAVE_CLK_GET_ACCURACY
+unsigned long clk_get_accuracy(struct clk *clk);
+#else
+static inline unsigned long clk_get_accuracy(struct clk *clk)
+{
+	return 0;
+}
+#endif
+
+/**
  * clk_prepare - prepare a clock source
  * @clk: clock source
  *
-- 
1.7.9.5


^ permalink raw reply related	[flat|nested] 3+ messages in thread
* [RFC PATCH 0/2] clk: add clk accuracy support
@ 2013-08-01 14:59 Boris BREZILLON
  2013-08-01 15:04 ` [RFC PATCH 1/2] clk: add clk accuracy retrieval support Boris BREZILLON
  0 siblings, 1 reply; 3+ messages in thread
From: Boris BREZILLON @ 2013-08-01 14:59 UTC (permalink / raw)
  To: Mike Turquette, Russell King
  Cc: linux-kernel, linux-arm-kernel, Boris BREZILLON

Hello,

This patch series is a proposal to add clock accuracy retrieval support to the
common clk framework.

The support of accuracy retrieval may benefit to the at91 platform (I explain
why in the following paragraphs).

I don't know if other platforms may benefit from this accuracy support. This
series is here to get feedbacks from other developpers/maintainers, and see if
this can be integrated in the clk framework.

Here is why at91 platform may need the clk accuracy informations:

AT91 SoCs provide a slow clock (32 KHz clock) which can be used as a clock
source for some peripherals (USART, TC blocks, ...).

This slow clock can be generated from 2 sources:
- a 32KHz internal RC with a poor accuracy (50000 ppm)
- a 32KHz external crystal oscillator

Most of the supported at91 boards (if not all) use the external 32KHz crystal
source except for the kizbox (the board I'm working with :)).
Most of you will say this is a bad hardware design and the hardware team
should have connected a crystal oscillator to the SoC instead of relying
on the unaccurate internal RC (and they are probably right).
But I can't change the hardware as it is already widely deployed.

What I'm proposing is to give clock users the ability to retrieve clocks
accuracies in order to choose the most accurate source (or at least discard
clocks with poor accuracy).

Could you tell me if this approach is right, and if other platforms/boards have
similar issues and would be interrested by this series ?

Best Regards,

Boris

Boris BREZILLON (2):
  clk: add clk accuracy retrieval support
  clk: add accuracy support for fixed clock

 Documentation/clk.txt                              |    4 +
 .../devicetree/bindings/clock/fixed-clock.txt      |    3 +
 drivers/clk/Kconfig                                |    4 +
 drivers/clk/clk-fixed-rate.c                       |   41 +++++++--
 drivers/clk/clk.c                                  |   91 +++++++++++++++++++-
 include/linux/clk-private.h                        |    1 +
 include/linux/clk-provider.h                       |   14 +++
 include/linux/clk.h                                |   17 ++++
 8 files changed, 166 insertions(+), 9 deletions(-)

-- 
1.7.9.5


^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2013-08-01 15:06 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2013-08-01 15:02 [RFC PATCH 1/2] clk: add clk accuracy retrieval support Boris BREZILLON
2013-08-01 15:06 ` boris brezillon
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2013-08-01 14:59 [RFC PATCH 0/2] clk: add clk accuracy support Boris BREZILLON
2013-08-01 15:04 ` [RFC PATCH 1/2] clk: add clk accuracy retrieval support Boris BREZILLON

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