[PATCH v1 2/3] clk: fractional-divider: Introduce NO_PRESCALER flag

Andy Shevchenko
2021-07-15T12:08:23Z

The newly introduced flag, when set, makes the flow to skip
the assumption that the caller will use an additional 2^scale
prescaler to get the desired clock rate.

Reported-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
drivers/clk/clk-fractional-divider.c | 2 +-
include/linux/clk-provider.h | 5 +++++
2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index 535d299af646..b2f9aae9f172 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -84,7 +84,7 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
* by (scale - fd->nwidth) bits.
*/
scale = fls_long(*parent_rate / rate - 1);
- if (scale > fd->nwidth)
+ if (scale > fd->nwidth && !(fd->flags & CLK_FRAC_DIVIDER_NO_PRESCALER))
rate <<= scale - fd->nwidth;

rational_best_approximation(rate, *parent_rate,
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index d83b829305c0..f74d0afe275f 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -1001,6 +1001,10 @@ struct clk_hw *devm_clk_hw_register_fixed_factor(struct device *dev,
* CLK_FRAC_DIVIDER_BIG_ENDIAN - By default little endian register accesses are
* used for the divider register. Setting this flag makes the register
* accesses big endian.
+ * CLK_FRAC_DIVIDER_NO_PRESCALER - By default the resulting rate may be shifted
+ * left by a few bits in case when the asked one is quite small to satisfy
+ * the desired range of denominator. If the caller wants to get the best
+ * rate without using an additional prescaler, this flag may be set.
*/
struct clk_fractional_divider {
struct clk_hw hw;
@@ -1022,6 +1026,7 @@ struct clk_fractional_divider {

#define CLK_FRAC_DIVIDER_ZERO_BASED BIT(0)
#define CLK_FRAC_DIVIDER_BIG_ENDIAN BIT(1)
+#define CLK_FRAC_DIVIDER_NO_PRESCALER BIT(2)

extern const struct clk_ops clk_fractional_divider_ops;
struct clk *clk_register_fractional_divider(struct device *dev,
--
2.30.2