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kernel
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linux
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>
authored by
Benoît Monin
and committed by
Thomas Bogendoerfer
fe9545bb
8ab1e58c
+9
-9
+9
-9
drivers/clk/clk-eyeq.c
+9
-9
drivers/clk/clk-eyeq.c
···
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static int eqc_pll_parse_registers(u32 r0, u32 r1, unsigned long *mult,
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unsigned long *div, unsigned long *acc)
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{
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-
u32 spread;
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unsigned long spread;
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if (r0 & PCSR0_BYPASS) {
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*mult = 1;
···
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/*
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* Spread spectrum.
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*
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* Spread is 1/1000 parts of frequency, accuracy is half of
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* that. To get accuracy, convert to ppb (parts per billion).
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* Spread is in 1/1024 parts of frequency. Clock accuracy
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* is half the spread value expressed in parts per billion.
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*
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* acc = spread * 1e6 / 2
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* with acc in parts per billion and,
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* spread in parts per thousand.
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* accuracy = (spread * 1e9) / (1024 * 2)
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*
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* Care is taken to avoid overflowing or losing precision.
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*/
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spread = FIELD_GET(PCSR1_SPREAD, r1);
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*acc = spread * 500000;
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*acc = DIV_ROUND_CLOSEST(spread * 1000000000, 1024 * 2);
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if (r1 & PCSR1_DOWN_SPREAD) {
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/*
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* Downspreading: the central frequency is half a
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* spread lower.
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*/
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*mult *= 2000 - spread;
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*div *= 2000;
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*mult *= 2048 - spread;
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*div *= 2048;
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/*
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* Previous operation might overflow 32 bits. If it