linux-kernel - [PATCH 5.18 03/88] ARM: dts: lan966x: fix sys

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Date:   Mon,  1 Aug 2022 13:46:17 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Michael Walle <michael@...le.cc>,
        Kavyasree Kotagiri <kavyasree.kotagiri@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>
Subject: [PATCH 5.18 03/88] ARM: dts: lan966x: fix sys_clk frequency

From: Michael Walle <michael@...le.cc>

commit ef0324b6415db6742bd632dc0dfbb8fbc111473b upstream.

The sys_clk frequency is 165.625MHz. The register reference of the
Generic Clock controller lists the CPU clock as 600MHz, the DDR clock as
300MHz and the SYS clock as 162.5MHz. This is wrong. It was first
noticed during the fan driver development and it was measured and
verified via the CLK_MON output of the SoC which can be configured to
output sys_clk/64.

The core PLL settings (which drives the SYS clock) seems to be as
follows:
  DIVF = 52
  DIVQ = 3
  DIVR = 1

With a refernce clock of 25MHz, this means we have a post divider clock
  Fpfd = Fref / (DIVR + 1) = 25MHz / (1 + 1) = 12.5MHz

The resulting VCO frequency is then
  Fvco = Fpfd * (DIVF + 1) * 2 = 12.5MHz * (52 + 1) * 2 = 1325MHz

And the output frequency is
  Fout = Fvco / 2^DIVQ = 1325MHz / 2^3 = 165.625Mhz

This all adds up to the constrains of the PLL:
    10MHz <= Fpfd <= 200MHz
    20MHz <= Fout <= 1000MHz
  1000MHz <= Fvco <= 2000MHz

Fixes: 290deaa10c50 ("ARM: dts: add DT for lan966 SoC and 2-port board pcb8291")
Signed-off-by: Michael Walle <michael@...le.cc>
Reviewed-by: Kavyasree Kotagiri <kavyasree.kotagiri@...rochip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
Link: https://lore.kernel.org/r/20220326194028.2945985-1-michael@walle.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm/boot/dts/lan966x.dtsi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/lan966x.dtsi b/arch/arm/boot/dts/lan966x.dtsi
index 3cb02fffe716..38e90a31d2dd 100644
--- a/arch/arm/boot/dts/lan966x.dtsi
+++ b/arch/arm/boot/dts/lan966x.dtsi
@@ -38,7 +38,7 @@ clocks {
 		sys_clk: sys_clk {
 			compatible = "fixed-clock";
 			#clock-cells = <0>;
-			clock-frequency = <162500000>;
+			clock-frequency = <165625000>;
 		};
 
 		cpu_clk: cpu_clk {
-- 
2.37.1