Question regarding HDMI Audio support on i.MX6 with vanilla kernel

[Russell King - ARM Linux]

On Mon, Nov 06, 2017 at 11:46:52AM +0000, Luís Mendes wrote:
> Hi Russell,
> 
> First of all sorry for posting this here, it isn't directly related with
> etnaviv, but results from the use of vanilla kernels.
> 
> I have been struggling with DW-HDMI to output audio... I've noticed that
> the driver is loaded and that alsa shows the audio device, but I am unable
> to get sound.
> No sound output even if I set the sound output with alsa or pacmd. Alsa
> shows no mixer or mute controls for the output.

You are probably missing the alsalib configuration file.  I've attached
it, which should be placed in /usr/share/alsa/cards/dw-hdmi-ahb-aud.conf

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#
# All PCM must be 24-bit for easy kernel conversion.
# IEC958 formatted output can be sent directly.
#
# Direct-to-hardware converting to 24-bit output.
#
dw-hdmi-ahb-aud.pcm.hw-s24le {
	@args [ CARD ]
	@args.CARD { type string }
	type linear
	slave.pcm { 
		type hw
		card $CARD
	}
	slave.format S24_LE
}

#
# Dmix hardware 24-bit output.
#
dw-hdmi-ahb-aud.pcm.dmix-s24le {
	@args [ CARD ]
	@args.CARD { type string }
	type plug
	slave.pcm { @func concat strings [ "dmix:" $CARD ",FORMAT=S24_LE" ] }
}

#
# Softvol with dmix output
#
dw-hdmi-ahb-aud.pcm.default {
	@args [ CARD ]
	@args.CARD { type string }
	type asym
	playback.pcm {
		type softvol
		slave.pcm {
			@func refer name { 
				@func concat strings [
					"cards."
					{ @func card_driver card $CARD }
					".pcm.dmix-s24le:CARD=" $CARD
				]
			}
		}
		control {
			name "PCM Playback Volume"
			card $CARD
		}
	}
}

#
# Common output path for front and surround outputs
#
dw-hdmi-ahb-aud.pcm.common.0 {
	@args [ CARD ]
	@args.CARD { type string }
	type asym
	playback.pcm {
		type softvol
		slave.pcm {
			@func refer name { 
				@func concat strings [
					"cards."
					{ @func card_driver card $CARD }
					".pcm.hw-s24le:CARD=" $CARD
				]
			}
		}
		control {
			name "PCM Playback Volume"
			card $CARD
		}
	}
}

<confdir:pcm/front.conf>

dw-hdmi-ahb-aud.pcm.front.0 cards.dw-hdmi-ahb-aud.pcm.common.0

# The mapping of ALSA channels to surround channels is very imprecise.
# ALSA uses a different terminology and speaker placement to the CEA
# surround positioning.  CEA has the positioning of:
#
#			LFE
#	FL	FLC	FC	FRC	FR
#
#
#	RL	RLC	RC	RRC	RR
#
# ALSA's idea is:
#
#			LFE
#		FL	C	FR
#
#		SL		SR
#
#		RL		RR
#
# We do our best to map between these representations.

<confdir:pcm/surround40.conf>

dw-hdmi-ahb-aud.pcm.surround40.0 {
	@args [ CARD ]
	@args.CARD { type string }
	type empty
	slave.pcm {
		@func refer
		name { 
			@func concat strings [
				"cards.dw-hdmi-ahb-aud.pcm.common.0:CARD="
				$CARD
			]
		}
	}
}

# surround 41 and surround50 are (annoyingly) mapped to surround51
# We could do without stacking two 'route' plugins on top of each other

<confdir:pcm/surround41.conf>
<confdir:pcm/surround50.conf>
<confdir:pcm/surround51.conf>

dw-hdmi-ahb-aud.pcm.surround51.0 {
	@args [ CARD ]
	@args.CARD { type string }
	type route
	slave.pcm {
		@func refer
		name { 
			@func concat strings [
				"cards.dw-hdmi-ahb-aud.pcm.common.0:CARD="
				$CARD
			]
		}
	}
	ttable.0.0 1.0 # FL  -> slave 0 -> hdmi 0 FL
	ttable.1.1 1.0 # FR  -> slave 1 -> hdmi 1 FR
	ttable.2.4 1.0 # RL  -> slave 4 -> hdmi 4 RL
	ttable.3.5 1.0 # RR  -> slave 5 -> hdmi 5 RR
	ttable.4.3 1.0 # C   -> slave 3 -> hdmi 3 FC 
	ttable.5.2 1.0 # LFE -> slave 2 -> hdmi 2 LFE
}

<confdir:pcm/surround71.conf>

dw-hdmi-ahb-aud.pcm.surround71.0 {
	@args [ CARD ]
	@args.CARD { type string }
	type route
	slave.pcm {
		@func refer
		name { 
			@func concat strings [
				"cards.dw-hdmi-ahb-aud.pcm.common.0:CARD="
				$CARD
			]
		}
	}
	slave.channels 8
	ttable.0.0 1.0 # FL  -> slave 0 -> hdmi 0 FL
	ttable.1.1 1.0 # FR  -> slave 1 -> hdmi 1 FR
	ttable.2.6 1.0 # RL  -> slave 6 -> hdmi 6 RLC/FLC
	ttable.3.7 1.0 # RR  -> slave 7 -> hdmi 7 RRC/FRC
	ttable.4.3 1.0 # C   -> slave 3 -> hdmi 3 FC
	ttable.5.2 1.0 # LFE -> slave 2 -> hdmi 2 LFE
	ttable.6.4 1.0 # SL  -> slave 4 -> hdmi 4 RL
	ttable.7.5 1.0 # SR  -> slave 5 -> hdmi 5 RR
}

<confdir:pcm/hdmi.conf>

dw-hdmi-ahb-aud.pcm.hdmi.0 {
	@args [ CARD AES0 AES1 AES2 AES3 ]
	@args.CARD { type string }
	@args.AES0 { type integer }
	@args.AES1 { type integer }
	@args.AES2 { type integer }
	@args.AES3 { type integer }
	type iec958
	slave.pcm {
		type hw
		card $CARD
	}
	slave.format IEC958_SUBFRAME_LE
	# $AES3 must be correct for some AV receivers to accept the stream
	status [ $AES0 $AES1 $AES2 $AES3 ]
}

<confdir:pcm/iec958.conf>

dw-hdmi-ahb-aud.pcm.iec958.0 cards.dw-hdmi-ahb-aud.pcm.hdmi.0