ASoC: rockchip: Add support for Digital Loopback

This patch add support for DMA-based digital loopback.

BACKGROUND
Audio Products with AEC require loopback for echo cancellation.
the hardware LP is not always available on some products, maybe
the HW limitation(such as internal acodec) or HW Cost-down.

This patch add support software DLP for such products.

Enable:

  CONFIG_SND_SOC_ROCKCHIP_DLP

  &i2s {
      rockchip,digital-loopback;
  };

Mode List:

  amixer contents
  numid=2,iface=MIXER,name='Software Digital Loopback Mode'
    ; type=ENUMERATED,access=rw------,values=1,items=7
    ; Item #0 'Disabled'
    ; Item #1 '2CH: 1 Loopback + 1 Mic'
    ; Item #2 '2CH: 1 Mic + 1 Loopback'
    ; Item #3 '2CH: 1 Mic + 1 Loopback-mixed'
    ; Item #4 '2CH: 2 Loopbacks'
    ; Item #5 '4CH: 2 Mics + 2 Loopbacks'
    ; Item #6 '4CH: 2 Mics + 1 Loopback-mixed'
    : values=0

Testenv:

wired SDO0 --> SDI0 directly to get external digital loopback
as reference.

Testcase: dlp.sh

  /#!/bin/sh

  item=0
  id=`amixer contents | grep "Software Digital Loopback" | \
      awk -F ',' '{print $1}'`

  items=`amixer contents | grep -A 1 "Software Digital Loopback" | \
         grep items | awk -F 'items=' '{print $2}'`

  echo "Software Digital Loopback: $id, items: $items"

  mode_chs() {
          case $1 in
          [0-4])
                  echo "2"
                  ;;
          [5-6])
                  echo "4"
                  ;;
          *)
                  echo "2"
                  ;;
          esac
  }

  while true
  do
          ch=`mode_chs $item`
          amixer -c 0 cset $id $item
          arecord -D hw:0,0 --period-size=1024 --buffer-size=4096 -r 48000 -c $ch -f s16_le \
                  -d 15 sine/dlp_$item.wav &
          sleep 2
          for i in $(seq 1 10)
          do
                  aplay -D hw:0,0 --period-size=1024 --buffer-size=8192 $((ch))ch.wav -d 1
          done
          pid=$(ps | egrep "aplay|arecord" | grep -v grep | awk '{print $1}' | sort -r)
          for p in $pid
          do
                  wait $p 2>/dev/null
          done
          item=$((item+1))
          if [ $item -ge $items ]; then
                  sleep 1
                  break
          fi
  done
  echo "Done"

Result:

do shell test and verify dlp_x.wav:

* Alignment: ~1 samples shift (loopback <-> mics).
* Integrity: no giltch, no data lost.
* AEC: align loopback and mics sample and do simple AEC, get clean
  waveform.

Logs:
...
numid=2,iface=MIXER,name='Software Digital Loopback Mode'
  ; type=ENUMERATED,access=rw------,values=1,items=7
  ; Item #0 'Disabled'
  ; Item #1 '2CH: 1 Loopback + 1 Mic'
  ; Item #2 '2CH: 1 Mic + 1 Loopback'
  ; Item #3 '2CH: 1 Mic + 1 Loopback-mixed'
  ; Item #4 '2CH: 2 Loopbacks'
  ; Item #5 '4CH: 2 Mics + 2 Loopbacks'
  ; Item #6 '4CH: 2 Mics + 1 Loopback-mixed'
  : values=2
Recording WAVE 'sine/dlp_2.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE '2ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
...
numid=2,iface=MIXER,name='Software Digital Loopback Mode'
  ; type=ENUMERATED,access=rw------,values=1,items=7
  ; Item #0 'Disabled'
  ; Item #1 '2CH: 1 Loopback + 1 Mic'
  ; Item #2 '2CH: 1 Mic + 1 Loopback'
  ; Item #3 '2CH: 1 Mic + 1 Loopback-mixed'
  ; Item #4 '2CH: 2 Loopbacks'
  ; Item #5 '4CH: 2 Mics + 2 Loopbacks'
  ; Item #6 '4CH: 2 Mics + 1 Loopback-mixed'
  : values=6
Recording WAVE 'sine/dlp_6.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Playing WAVE '4ch.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Channels 4
Done

Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Change-Id: I5772f0694f7a14a0f0bd1f0777b6c4cdbd781a64

sound/soc/rockchip/Kconfig

@@ -7,6 +7,13 @@ config SND_SOC_ROCKCHIP
 	  the Rockchip SoCs' Audio interfaces. You will also need to
 	  select the audio interfaces to support below.
 
+config SND_SOC_ROCKCHIP_DLP
+	tristate "Rockchip Digital Loopback Driver"
+	depends on SND_SOC_ROCKCHIP
+	help
+	  Say Y or M if you want to add support for DLP driver for
+	  Rockchip DMA-Based Digital Loopback.
+
 config SND_SOC_ROCKCHIP_I2S
 	tristate "Rockchip I2S Device Driver"
 	depends on CLKDEV_LOOKUP && SND_SOC_ROCKCHIP

sound/soc/rockchip/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 # ROCKCHIP Platform Support
+snd-soc-rockchip-dlp-objs := rockchip_dlp.o
 snd-soc-rockchip-i2s-objs := rockchip_i2s.o
 snd-soc-rockchip-i2s-tdm-objs := rockchip_i2s_tdm.o
 snd-soc-rockchip-multi-dais-objs := rockchip_multi_dais.o rockchip_multi_dais_pcm.o
@@ -14,6 +15,7 @@ snd-soc-rockchip-vad-$(CONFIG_ARM64) += vad_preprocess_arm64.o
 snd-soc-rockchip-vad-$(CONFIG_ARM) += vad_preprocess_arm.o
 endif
 
+obj-$(CONFIG_SND_SOC_ROCKCHIP_DLP) += snd-soc-rockchip-dlp.o
 obj-$(CONFIG_SND_SOC_ROCKCHIP_I2S) += snd-soc-rockchip-i2s.o
 obj-$(CONFIG_SND_SOC_ROCKCHIP_I2S_TDM) += snd-soc-rockchip-i2s-tdm.o
 obj-$(CONFIG_SND_SOC_ROCKCHIP_MULTI_DAIS) += snd-soc-rockchip-multi-dais.o