clk: add clk accuracy retrieval support

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>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 7e59253b8603..16d182c28ce6 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);
 };
 
@@ -433,6 +443,7 @@ struct clk *clk_get_parent_by_index(struct clk *clk, u8 index);
 unsigned int __clk_get_enable_count(struct clk *clk);
 unsigned int __clk_get_prepare_count(struct clk *clk);
 unsigned long __clk_get_rate(struct clk *clk);
+unsigned long __clk_get_accuracy(struct clk *clk);
 unsigned long __clk_get_flags(struct clk *clk);
 bool __clk_is_prepared(struct clk *clk);
 bool __clk_is_enabled(struct clk *clk);