linux-kernel - [PATCH 08/13] clk: eyeq: Adjust PLL accuracy computation

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Message-Id: <20251217-eyeq6lplus-v1-8-e9cdbd3af4c2@bootlin.com>
Date: Wed, 17 Dec 2025 14:35:58 +0100
From: Benoît Monin <benoit.monin@...tlin.com>
To: Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Gregory CLEMENT <gregory.clement@...tlin.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>, 
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>, 
 Linus Walleij <linusw@...nel.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, linux-mips@...r.kernel.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org, 
 Benoît Monin <benoit.monin@...tlin.com>
Subject: [PATCH 08/13] 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@...tlin.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 182b408b6aa4..8fb32f365f3d 100644
--- 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

-- 
2.52.0