Hello,
Sorry for the noise, but I didn't get any feedback on this patch series.
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 :)).
It probably comes from a bad hardware design (hardware team should have
connected a crystal oscillator to the SoC instead of relying on the unaccurate
internal RC).
Anyway, 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 | 43 +++++++--
drivers/clk/clk.c | 92 +++++++++++++++++++-
include/linux/clk-private.h | 1 +
include/linux/clk-provider.h | 14 +++
include/linux/clk.h | 17 ++++
8 files changed, 168 insertions(+), 10 deletions(-)
--
1.7.9.5
This patch adds support for accuracy retrieval on fixed clocks.
It also adds a new dt property called 'clock-accuracy' to define the clock
accuracy.
This can be usefull for oscillator (RC, crystal, ...) definitions which are
always given an accuracy characteristic.
Signed-off-by: Boris BREZILLON <[email protected]>
---
.../devicetree/bindings/clock/fixed-clock.txt | 3 ++
drivers/clk/clk-fixed-rate.c | 43 +++++++++++++++++---
include/linux/clk-provider.h | 3 ++
3 files changed, 43 insertions(+), 6 deletions(-)
diff --git a/Documentation/devicetree/bindings/clock/fixed-clock.txt b/Documentation/devicetree/bindings/clock/fixed-clock.txt
index 0b1fe78..48ea0ad 100644
--- a/Documentation/devicetree/bindings/clock/fixed-clock.txt
+++ b/Documentation/devicetree/bindings/clock/fixed-clock.txt
@@ -10,6 +10,8 @@ Required properties:
- clock-frequency : frequency of clock in Hz. Should be a single cell.
Optional properties:
+- clock-accuracy : accuracy of clock in ppb (parts per billion).
+ Should be a single cell.
- gpios : From common gpio binding; gpio connection to clock enable pin.
- clock-output-names : From common clock binding.
@@ -18,4 +20,5 @@ Example:
compatible = "fixed-clock";
#clock-cells = <0>;
clock-frequency = <1000000000>;
+ clock-accuracy = <100>;
};
diff --git a/drivers/clk/clk-fixed-rate.c b/drivers/clk/clk-fixed-rate.c
index 1ed591a..0fc56ab 100644
--- a/drivers/clk/clk-fixed-rate.c
+++ b/drivers/clk/clk-fixed-rate.c
@@ -34,22 +34,31 @@ static unsigned long clk_fixed_rate_recalc_rate(struct clk_hw *hw,
return to_clk_fixed_rate(hw)->fixed_rate;
}
+static unsigned long clk_fixed_rate_recalc_accuracy(struct clk_hw *hw,
+ unsigned long parent_accuracy)
+{
+ return to_clk_fixed_rate(hw)->fixed_accuracy;
+}
+
const struct clk_ops clk_fixed_rate_ops = {
.recalc_rate = clk_fixed_rate_recalc_rate,
+ .recalc_accuracy = clk_fixed_rate_recalc_accuracy,
};
EXPORT_SYMBOL_GPL(clk_fixed_rate_ops);
/**
- * clk_register_fixed_rate - register fixed-rate clock with the clock framework
+ * clk_register_fixed_rate_with_accuracy - register fixed-rate clock with the
+ * clock framework
* @dev: device that is registering this clock
* @name: name of this clock
* @parent_name: name of clock's parent
* @flags: framework-specific flags
* @fixed_rate: non-adjustable clock rate
+ * @fixed_accuracy: non-adjustable clock rate
*/
-struct clk *clk_register_fixed_rate(struct device *dev, const char *name,
- const char *parent_name, unsigned long flags,
- unsigned long fixed_rate)
+struct clk *clk_register_fixed_rate_with_accuracy(struct device *dev,
+ const char *name, const char *parent_name, unsigned long flags,
+ unsigned long fixed_rate, unsigned long fixed_accuracy)
{
struct clk_fixed_rate *fixed;
struct clk *clk;
@@ -70,16 +79,33 @@ struct clk *clk_register_fixed_rate(struct device *dev, const char *name,
/* struct clk_fixed_rate assignments */
fixed->fixed_rate = fixed_rate;
+ fixed->fixed_accuracy = fixed_accuracy;
fixed->hw.init = &init;
/* register the clock */
clk = clk_register(dev, &fixed->hw);
-
if (IS_ERR(clk))
kfree(fixed);
return clk;
}
+EXPORT_SYMBOL_GPL(clk_register_fixed_rate_with_accuracy);
+
+/**
+ * clk_register_fixed_rate - register fixed-rate clock with the clock framework
+ * @dev: device that is registering this clock
+ * @name: name of this clock
+ * @parent_name: name of clock's parent
+ * @flags: framework-specific flags
+ * @fixed_rate: non-adjustable clock rate
+ */
+struct clk *clk_register_fixed_rate(struct device *dev, const char *name,
+ const char *parent_name, unsigned long flags,
+ unsigned long fixed_rate)
+{
+ return clk_register_fixed_rate_with_accuracy(dev, name, parent_name,
+ flags, fixed_rate, 0);
+}
EXPORT_SYMBOL_GPL(clk_register_fixed_rate);
#ifdef CONFIG_OF
@@ -91,13 +117,18 @@ void of_fixed_clk_setup(struct device_node *node)
struct clk *clk;
const char *clk_name = node->name;
u32 rate;
+ u32 accuracy = 0;
if (of_property_read_u32(node, "clock-frequency", &rate))
return;
+ of_property_read_u32(node, "clock-accuracy", &accuracy);
+
of_property_read_string(node, "clock-output-names", &clk_name);
- clk = clk_register_fixed_rate(NULL, clk_name, NULL, CLK_IS_ROOT, rate);
+ clk = clk_register_fixed_rate_with_accuracy(NULL, clk_name, NULL,
+ CLK_IS_ROOT, rate,
+ accuracy);
if (!IS_ERR(clk))
of_clk_add_provider(node, of_clk_src_simple_get, clk);
}
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 942811d..67878a4 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -212,6 +212,9 @@ extern const struct clk_ops clk_fixed_rate_ops;
struct clk *clk_register_fixed_rate(struct device *dev, const char *name,
const char *parent_name, unsigned long flags,
unsigned long fixed_rate);
+struct clk *clk_register_fixed_rate_with_accuracy(struct device *dev,
+ const char *name, const char *parent_name, unsigned long flags,
+ unsigned long fixed_rate, unsigned long fixed_accuracy);
void of_fixed_clk_setup(struct device_node *np);
--
1.7.9.5
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 <[email protected]>
---
Documentation/clk.txt | 4 ++
drivers/clk/Kconfig | 4 ++
drivers/clk/clk.c | 92 ++++++++++++++++++++++++++++++++++++++++--
include/linux/clk-private.h | 1 +
include/linux/clk-provider.h | 11 +++++
include/linux/clk.h | 17 ++++++++
6 files changed, 125 insertions(+), 4 deletions(-)
diff --git a/Documentation/clk.txt b/Documentation/clk.txt
index 3aeb5c4..dc52da1 100644
--- a/Documentation/clk.txt
+++ b/Documentation/clk.txt
@@ -77,6 +77,8 @@ 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);
};
@@ -202,6 +204,8 @@ optional or must be evaluated on a case-by-case basis.
.set_parent | | | n | y | n |
.get_parent | | | n | y | n |
| | | | | |
+.recalc_rate | | | | | |
+ | | | | | |
.init | | | | | |
-----------------------------------------------------------
[1] either one of round_rate or determine_rate is required.
diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 279407a..4d12ae7 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 a004769..6a8f3ef 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)
@@ -602,6 +609,11 @@ 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;
@@ -1016,6 +1028,59 @@ 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)
@@ -1545,6 +1610,7 @@ 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);
}
@@ -1615,6 +1681,9 @@ 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);
@@ -1724,6 +1793,21 @@ 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 8138c94..accb517 100644
--- a/include/linux/clk-private.h
+++ b/include/linux/clk-private.h
@@ -41,6 +41,7 @@ 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 73bdb69..942811d 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -29,6 +29,7 @@
#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_SET_RATE_NO_REPARENT BIT(7) /* don't re-parent on rate change */
+#define CLK_GET_ACCURACY_NOCACHE BIT(8) /* do not use the cached clk accuracy */
struct clk_hw;
@@ -108,6 +109,13 @@ 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,
@@ -139,6 +147,8 @@ 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);
};
@@ -194,6 +204,7 @@ 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..2fe3b54 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