[D18] add Bluetooth audio support

* enabled at u-boot: seco_config tool
* audio over SAI3 interface
  * SAI3 --> carrier board or onboard bluetooth (I2S2 SMARC | AUDIO BT)
* Filesystem support --> pulseaudio + bluez5
  * Yocto packages:
    pulseaudio-server pulseaudio-module-cli pulseaudio-misc
    pulseaudio-module-device-manager bluez5-noinst-tools bluez5-obex
    bluez5-testtools pulseaudio-module-bluetooth-discover
    pulseaudio-module-bluetooth-policy pulseaudio-module-bluez5-discover
    pulseaudio-module-bluez5-device pulseaudio-module-switch-on-connect
    pulseaudio-module-loopback
* Test details:
  root@seco-imx8mp-d18:~# pulseaudio -D
  root@seco-imx8mp-d18:~# bluetoothctl
  [bluetooth]# default-agent
  [bluetooth]# power on
  [bluetooth]# scan on
  ...
  Device 74:45:CE:40:2B:DD WH-CH510
  ...
  [bluetooth]# scan off
  [bluetooth]# trust 74:45:CE:40:2B:DD
  [bluetooth]# pair 74:45:CE:40:2B:DD
  [bluetooth]# connect 74:45:CE:40:2B:DD
  [WH-CH510]# info
  Device 74:45:CE:40:2B:DD (public)
    Name: WH-CH510
    Alias: WH-CH510
    Class: 0x00240404
    ...
  [WH-CH510]# exit
  root@seco-imx8mp-d18:~# pactl list sinks short | awk '{print $2}'
  root@seco-imx8mp-d18:~# paplay -d bluez_sink.74_45_CE_40_2B_DD.a2dp_sink test.wav

arch/arm64/boot/dts/seco/overlays/Makefile

 DTC_FLAGS ?= -@ -H epapr
 
+dtbo-$(CONFIG_ARCH_MXC) += \
+	seco-imx8mp-d18-audio-btsco.dtbo
+
 targets += dtbs dtbs_install
 targets += $(dtbo-y)
 

arch/arm64/boot/dts/seco/overlays/seco-imx8mp-d18-audio-btsco-overlay.dts

+/*
+ * Copyright 2021 SECO
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <dt-bindings/clock/imx8mp-clock.h>
+
+/dts-v1/;
+/plugin/;
+
+/ {
+	compatible = "fsl,imx8mp-evk", "seco,imx8mp-d18", "fsl,imx8mp";
+
+/*  __________________________________________________________________________
+ * |                                                                          |
+ * |                               AUDIO BLUETOOTH                            |
+ * |__________________________________________________________________________|
+ */
+
+	fragment@0 {
+		target = <&bt_sco_codec>;
+		__overlay__ {
+			#sound-dai-cells = <1>;
+			compatible = "linux,bt-sco";
+		};
+	};
+
+	fragment@1 {
+		target = <&soundbtsco>;
+		__overlay__ {
+			status = "okay";
+			compatible = "simple-audio-card";
+			simple-audio-card,name = "bt-sco-audio";
+			simple-audio-card,format = "dsp_a";
+			simple-audio-card,bitclock-inversion;
+			simple-audio-card,frame-master = <&btcpu>;
+			simple-audio-card,bitclock-master = <&btcpu>;
+
+			btcpu: simple-audio-card,cpu {
+				sound-dai = <&sai3>;
+				dai-tdm-slot-num = <2>;
+				dai-tdm-slot-width = <16>;
+			};
+
+			simple-audio-card,codec {
+				sound-dai = <&bt_sco_codec 1>;
+			};
+		};
+	};
+
+	fragment@2 {
+		target = <&sai3>;
+		__overlay__ {
+			#sound-dai-cells = <0>;
+			pinctrl-names = "default";
+			pinctrl-0 = <&pinctrl_sai3>;
+			assigned-clocks = <&clk IMX8MP_CLK_SAI3>;
+			assigned-clock-parents = <&clk IMX8MP_AUDIO_PLL1_OUT>;
+			assigned-clock-rates = <12288000>;
+			status = "okay";
+		};
+	};
+
+};

arch/arm64/boot/dts/seco/seco-imx8mp-d18.dts

@@ -101,7 +101,7 @@ reg_audio: regulator-soc-audio {
 	bt_sco_codec: bt_sco_codec {
 	};
 
-	sound-bt-sco {
+	soundbtsco: sound-bt-sco {
 	};
 
 	sound {
@@ -896,9 +896,6 @@ MX8MP_IOMUXC_SAI3_TXFS__AUDIOMIX_SAI3_TX_SYNC	0xd6
 			MX8MP_IOMUXC_SAI3_TXC__AUDIOMIX_SAI3_TX_BCLK	0xd6
 			MX8MP_IOMUXC_SAI3_RXD__AUDIOMIX_SAI3_RX_DATA00	0xd6
 			MX8MP_IOMUXC_SAI3_TXD__AUDIOMIX_SAI3_TX_DATA00	0xd6
-			MX8MP_IOMUXC_SAI3_MCLK__AUDIOMIX_SAI3_MCLK	0xd6
-			MX8MP_IOMUXC_SAI3_RXFS__GPIO4_IO28		0xd6
-			MX8MP_IOMUXC_SAI3_RXC__GPIO4_IO29		0xd6
 		>;
 	};