clk: eyeq: Adjust PLL accuracy computation

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>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

diff --git a/drivers/clk/clk-eyeq.c b/drivers/clk/clk-eyeq.c
index 5166b65382a965108d705cade09ec759d988a72f..11df9f167b5960c02156c7606f58b330ef7ec4ed 100644 (file)
--- a/drivers/clk/clk-eyeq.c
+++ b/drivers/clk/clk-eyeq.c
@@ -163,7 +163,7 @@ 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;
@@ -195,23 +195,23 @@ 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