[V3,2/6] clk: bcm2835: clamp clock divider to highest integer only

Commit Message

Martin Sperl Jan. 14, 2016, 1:45 p.m. UTC

From: Martin Sperl <[e-mail]>

The clock divider calculation right now clamps the
divider to the highest possible fractional divider.
So typically (BIT(div_int_bits) - 1) + 4095 / 4096.

As the fractional clock divider is alterating between
(Fosc / div_int) and (Fosc / (div_int + 1))
the divider will overflow for the (div_int + 1) case.
As with the "underflow" case we have seen for (div < 2),
we can assume that the same applies on the upper limit
as well.

So this patch will instead clamp to the divider to
(BIT(div_int_bits) - 1)

Signed-off-by: Martin Sperl <[e-mail]>
---
 drivers/clk/bcm/clk-bcm2835.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--
1.7.10.4

Patch

diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
index 10e97b7..3d6490f 100644
--- a/drivers/clk/bcm/clk-bcm2835.c
+++ b/drivers/clk/bcm/clk-bcm2835.c
@@ -1182,9 +1182,9 @@  static u32 bcm2835_clock_choose_div(struct clk_hw *hw,
 	/* divider must be >= 2 */
 	div = max_t(u32, div, (2 << CM_DIV_FRAC_BITS));

-	/* clamp to max divider allowed */
+	/* clamp to max divider allowed - max is integer divider */
 	div = min_t(u32, div, GENMASK(data->int_bits + CM_DIV_FRAC_BITS - 1,
-				      CM_DIV_FRAC_BITS - data->frac_bits));
+				      CM_DIV_FRAC_BITS));

 	return div;
 }