[PATCH v1] arm64: dts: k3-am625-verdin: enable nau8822 pll

[Andrejs Cainikovs]

From: Andrejs Cainikovs <andrejs.cainikovs at toradex.com>

In current configuration, nau8822 codec on development carrier board
provides distorted audio output. This happens due to reference clock
is fixed to 25MHz and no PLL is enabled. Following is the calculation
of deviation error for different frequencies:

44100Hz:

fs = 256 (fixed)
prescaler = 2
target frequency = 44100 * 256 * 2 = 22579200
deviation = 22579200 vs 25000000 = 9.6832%

48000Hz:

fs = 256 (fixed)
prescaler = 2
target frequency = 48000 * 256 * 2 = 24576000
deviation = 24576000 vs 25000000 = 1.696%

Enabling nau822 PLL via providing mclk-fs property to simple-audio-card
configures clocks properly, but also adjusts audio reference clock
(mclk), which in case of TI AM62 should be avoided, as it only
supports 25MHz output [1][2].

This change enables PLL on nau8822 by providing mclk-fs, and moves
away audio reference clock from DAI configuration, which prevents
simple-audio-card to adjust it before every playback [3].

[1]: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1175479/processor-sdk-am62x-output-audio_ext_refclk0-as-mclk-for-codec-and-mcbsp/4444986#4444986
[2]: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1188051/am625-audio_ext_refclk1-clock-output---dts-support/4476322#4476322
[3]: sound/soc/generic/simple-card-utils.c#L441

Signed-off-by: Andrejs Cainikovs <andrejs.cainikovs at toradex.com>
---
This patch requires https://lore.kernel.org/all/20240409121719.337709-1-andrejs.cainikovs@gmail.com/ to be applied,
if not the audio will just stop working because no code will ever enable the required clock to the codec.
---
 arch/arm64/boot/dts/ti/k3-am62-verdin-dev.dtsi | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/ti/k3-am62-verdin-dev.dtsi b/arch/arm64/boot/dts/ti/k3-am62-verdin-dev.dtsi
index 74eec1a1abca..5c1284b802ad 100644
--- a/arch/arm64/boot/dts/ti/k3-am62-verdin-dev.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-am62-verdin-dev.dtsi
@@ -14,6 +14,7 @@ sound {
 		simple-audio-card,bitclock-master = <&codec_dai>;
 		simple-audio-card,format = "i2s";
 		simple-audio-card,frame-master = <&codec_dai>;
+		simple-audio-card,mclk-fs = <256>;
 		simple-audio-card,name = "verdin-nau8822";
 		simple-audio-card,routing =
 			"Headphones", "LHP",
@@ -34,7 +35,6 @@ sound {
 			"Line", "Line In";
 
 		codec_dai: simple-audio-card,codec {
-			clocks = <&audio_refclk1>;
 			sound-dai = <&nau8822_1a>;
 		};
 
@@ -107,6 +107,8 @@ nau8822_1a: audio-codec at 1a {
 		reg = <0x1a>;
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_i2s1_mclk>;
+		clock-names = "mclk";
+		clocks = <&audio_refclk1>;
 		#sound-dai-cells = <0>;
 	};
 
-- 
2.34.1