linux-kernel - [PATCH v2 2/2] arm64: dts: rockchip: set codec system-clock-fixed on px30-ringneck-haikou

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Message-Id: <20230823131651.586934-2-jakob.unterwurzacher@theobroma-systems.com>
Date:   Wed, 23 Aug 2023 15:16:51 +0200
From:   Jakob Unterwurzacher <jakobunt@...il.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>
Cc:     jakob.unterwurzacher@...obroma-systems.com,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] arm64: dts: rockchip: set codec system-clock-fixed on px30-ringneck-haikou

Having sgtl5000_clk defines as "fixed-clock" is not enough to prevent
the dai subsystem from overwriting the frequency via sgtl5000_set_dai_sysclk.

Setting system-clock-fixed does the job, and now a 1kHz sine wave
comes out as actually 1kHz, no matter the sample rate of the source.

Testcase: These should sound the same:

 speaker-test -r 48000 -t sine -f 1000
 speaker-test -r 24000 -t sine -f 1000

Also remove the clock link here as having it in sgtl5000 and
sgtl5000_codec causes duplicate clock unprepares with associated
backtrace.

Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher@...obroma-systems.com>
---
 arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts b/arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts
index dafeef0c2dab..2cad02096271 100644
--- a/arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts
+++ b/arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts
@@ -72,8 +72,10 @@ i2s0-sound {
 		simple-audio-card,bitclock-master = <&sgtl5000_codec>;
 
 		sgtl5000_codec: simple-audio-card,codec {
-			clocks = <&sgtl5000_clk>;
 			sound-dai = <&sgtl5000>;
+			// Prevent the dai subsystem from overwriting the clock
+			// frequency. We are using a fixed-frequency oscillator.
+			system-clock-fixed;
 		};
 
 		simple-audio-card,cpu {
-- 
2.39.2