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

["Benoît Monin" <benoit.monin@bootlin.com>]

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