Quoting Boris BREZILLON (2013-10-13 10:17:10)
> 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@xxxxxxxxxxx>
> ---
> 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 | | | | | |
s/recalc_rate/recalc_accuracy/
> + | | | | | |
> .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
> +
This sort of thing gets messy. For platforms converted to common struct
clk we select HAVE_CLK_PREPARE and we let legacy platforms select it on
a case-by-case basis.
For something like HAVE_CLK_GET_ACCURACY I am inclined to only add it
for platforms converted to the common struct clk and not even expose it
to legacy clock framework implementations. In those cases the call to
clk_get_accuracy would return -EINVAL or -EPERM or something.
Russell, any thoughts on that approach?
> 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);
I think that there is some overlap between recalculating the accuracy
here and simply getting it. You only provide clk_get_accuracy and it
serves both purposes. It would be better if clk_recalc_accuracy walked
the subtree of children and if clk_get_accuracy simply returned a cached
value.
> +
> + 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);
Similar to the above statement. Why do this here? We do this for rates
since calls to clk_get_rate will return the cached rate (unless the
NOCACHE flag is set). But since a call to clk_get_accuracy will always
recalculate it then there is no benefit to doing that here.
> __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);
Ditto.
Regards,
Mike
> +
> /* 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
>
>
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