[PATCH v4 08/13] clk: eyeq: Adjust PLL accuracy computation

Benoît Monin
2026-03-16T15:26:06Z

The spread spectrum of the PLL found in eyeQ OLB is in 1/1024 parts of the
frequency, not in 1/1000, so adjust the computation of the accuracy. Also
correct the downspreading to match.

Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
---
drivers/clk/clk-eyeq.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/clk/clk-eyeq.c b/drivers/clk/clk-eyeq.c
index 904d7d77d415..abffa46364f5 100644
--- a/drivers/clk/clk-eyeq.c
+++ b/drivers/clk/clk-eyeq.c
@@ -164,7 +164,7 @@ static void eqc_pll_downshift_factors(unsigned long *mult, unsigned long *div)
static int eqc_pll_parse_registers(u32 r0, u32 r1, unsigned long *mult,
unsigned long *div, unsigned long *acc)
{
- u32 spread;
+ unsigned long spread;

if (r0 & PCSR0_BYPASS) {
*mult = 1;
@@ -196,23 +196,23 @@ static int eqc_pll_parse_registers(u32 r0, u32 r1, unsigned long *mult,
/*
* Spread spectrum.
*
- * Spread is 1/1000 parts of frequency, accuracy is half of
- * that. To get accuracy, convert to ppb (parts per billion).
+ * Spread is in 1/1024 parts of frequency. Clock accuracy
+ * is half the spread value expressed in parts per billion.
*
- * acc = spread * 1e6 / 2
- * with acc in parts per billion and,
- * spread in parts per thousand.
+ * accuracy = (spread * 1e9) / (1024 * 2)
+ *
+ * Care is taken to avoid overflowing or losing precision.
*/
spread = FIELD_GET(PCSR1_SPREAD, r1);
- *acc = spread * 500000;
+ *acc = DIV_ROUND_CLOSEST(spread * 1000000000, 1024 * 2);

if (r1 & PCSR1_DOWN_SPREAD) {
/*
* Downspreading: the central frequency is half a
* spread lower.
*/
- *mult *= 2000 - spread;
- *div *= 2000;
+ *mult *= 2048 - spread;
+ *div *= 2048;

/*
* Previous operation might overflow 32 bits. If it

--
2.53.0