Re: [PATCH v2 1/2] clk: add clk accuracy retrieval support

Uwe Kleine-König
2013-12-02T07:51:07Z

Hello,

On Wed, Nov 27, 2013 at 01:44:44PM +0100, Boris BREZILLON wrote:
> 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/clk.c | 109 ++++++++++++++++++++++++++++++++++++++++--
> include/linux/clk-private.h | 1 +
> include/linux/clk-provider.h | 11 +++++
> include/linux/clk.h | 17 +++++++
> 5 files changed, 138 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/clk.txt b/Documentation/clk.txt
> index 3aeb5c4..eb20198 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_accuracy| | | | | |
> + | | | | | |
> .init | | | | | |
> -----------------------------------------------------------
> [1] either one of round_rate or determine_rate is required.
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 2cf2ea6..4b0c1bc 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 +609,28 @@ out:
> return ret;
> }
>
> +unsigned long __clk_get_accuracy(struct clk *clk)
> +{
> + unsigned long ret;
> +
> + if (!clk) {
> + ret = 0;
> + goto out;
> + }
> +
> + ret = clk->accuracy;
> +
> + if (clk->flags & CLK_IS_ROOT)
> + goto out;
> +
> + if (!clk->parent)
> + ret = 0;
Why do you need this? Wouldn't it be enough to assert clk->accuracy
being 0 in this case?

> +out:
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(__clk_get_accuracy);
> +
> unsigned long __clk_get_flags(struct clk *clk)
> {
> return !clk ? 0 : clk->flags;
> @@ -1016,6 +1045,59 @@ 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)
There is no msg parameter in this function.

> + * 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.
> + */
> +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)
> @@ -1551,6 +1633,7 @@ 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);
> }
>
> @@ -1621,6 +1704,9 @@ 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);
> +
Would it make sense to move this call into the if (ret) below? The rate
is only recalculated there, too.

> /* propagate rate recalculation accordingly */
> if (ret)
> __clk_recalc_rates(clk, ABORT_RATE_CHANGE);

Best regards
Uwe

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