[RFC 5/9] clk: bcm2835: prefer clocks that use integer dividers
kernel at martin.sperl.org
kernel at martin.sperl.org
Tue Jan 19 06:51:36 PST 2016
From: Martin Sperl <kernel at martin.sperl.org>
To reduce possible jitter prefer integer dividers over
fractional dividers.
Signed-off-by: Martin Sperl <kernel at martin.sperl.org>
---
drivers/clk/bcm/clk-bcm2835.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
index f1ab525..e5313ba 100644
--- a/drivers/clk/bcm/clk-bcm2835.c
+++ b/drivers/clk/bcm/clk-bcm2835.c
@@ -1686,6 +1686,24 @@ static int bcm2835_clock_determine_rate_set(struct clk_rate_request *req,
return 0;
}
+static int bcm2835_clock_determine_integer_rate(struct clk_hw *hw,
+ struct clk_rate_request *req,
+ struct bcm2835_rates *rates,
+ size_t rate_cnt)
+{
+ size_t i;
+
+ /* find first matching */
+ for (i = 0; i < rate_cnt; i++) {
+ if (!divmash_get_divf(rates[i].dmash))
+ return bcm2835_clock_determine_rate_set(req,
+ &rates[i]);
+ }
+
+ /* nothing found */
+ return -EINVAL;
+}
+
static int bcm2835_clock_determine_closest_rate(struct clk_hw *hw,
struct clk_rate_request *req,
struct bcm2835_rates *rates,
@@ -1729,6 +1747,7 @@ static int bcm2835_clock_determine_rate(struct clk_hw *hw,
struct bcm2835_rates rates[BIT(CM_SRC_BITS)];
size_t i, rate_cnt = 0;
divmash dm;
+ int err;
/* fill in rates */
for (i = 0; i < clk_hw_get_num_parents(hw); ++i) {
@@ -1745,7 +1764,12 @@ static int bcm2835_clock_determine_rate(struct clk_hw *hw,
rate_cnt++;
}
- /* choose the "closest" one */
+ /* find integer rates with preference */
+ err = bcm2835_clock_determine_integer_rate(hw, req, rates, rate_cnt);
+ if (!err)
+ return 0;
+
+ /* otherwise choose the "closest" one */
return bcm2835_clock_determine_closest_rate(hw, req, rates,
rate_cnt);
}
--
1.7.10.4
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