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clk: eyeq: Adjust PLL accuracy computation

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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>
This commit is contained in:
Benoît Monin
2026-03-16 16:25:45 +01:00
committed by Thomas Bogendoerfer
parent 8ab1e58ca9
commit fe9545bbc3
1 changed files with 9 additions and 9 deletions
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18
drivers/clk/clk-eyeq.c
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@@ -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