CM4S: First boot display on drm/card0, subsequent boots on drm/card1, and PCM/Master audio volume out of sync

[JinShil]

Describe the bug

I'm using 3 different Raspberry Pi Compute Modules (CM3+, CM4S, and CM4) devices. All are nearly identical in features with only one connected HDMI display. The CM3+ and CM4 work as expected but the CM4S has different behavior on the first boot, compared with subsequent boots.

CM3+ (Good)

When booting the CM3+, ls /sys/class/drm/ reports...

card0  card0-HDMI-A-1  card0-Writeback-1  renderD128  version

... with the display on card0 as there is only one card. As expected /sys/class/drm/card0-HDMI-A-1/edid reports the EDID of my display.

When adjusting the Master volume slider in alsamixer, it also adjusts the PCM volume slider reported in sudo alsamixer, and vise-versa. This is important for my use case; the two should be in sync -- and they are.

With subsequent boots, the system remains the same, as expected.

/boot/config.txt

# LCD display settings
hdmi_group=2
hdmi_mode=87
hdmi_cvt 800 480 60 6 0 0 0

# Enable the I2C port
dtparam=i2c_arm=on

# RTC
dtoverlay=i2c-rtc,ds3231

# Serial ports
enable_uart=1
core_freq=250
dtoverlay=uart1,txd1_pin=32,rxd1_pin=33

# Audio
dtparam=audio=on
dtoverlay=audremap,pins_40_41

# Enable DRM VC4 V3D driver
dtoverlay=vc4-kms-v3d,noaudio

CM4 (Good)

When booting the CM4, ls /sys/class/drm/ reports...

card0  card1  card1-HDMI-A-1  card1-HDMI-A-2  card1-Writeback-1  renderD128  version

... with the display on card1. As expected /sys/class/drm/card1-HDMI-A-1/edid reports the EDID of my display. /sys/class/drm/card1-HDMI-A-2/edid exists, but is empty as there is only one display connected.

When adjusting the Master volume slider in alsamixer, it also adjusts the PCM volume slider reported in sudo alsamixer, and vise-versa. The two should be in sync -- and they are.

With subsequent boots, the system remains the same, as expected.

/boot/config.txt

# LCD display settings
hdmi_group=2
hdmi_mode=87
hdmi_cvt 800 480 60 6 0 0 0

# Disable pcie
dtparam=pcie=off

# RTC
dtparam=i2c_arm=on
dtoverlay=i2c-rtc,ds3231

# Serial ports
dtoverlay=disable-bt
dtparam=uart0=on
dtoverlay=uart2,txd2_pin=0,rxd2_pin=1

# Audio
dtparam=audio=on
dtoverlay=audremap,pins_12_13

# USB peripherals
dtoverlay=dwc2,dr_mode=host

# Enable the VC4 display driver
dtoverlay=vc4-kms-v3d,noaudio

CM4S (Bad)

When booting the CM4S the first time, ls /sys/class/drm/ reports...

card0  card0-HDMI-A-1  card0-Writeback-1  card1  renderD128  version

... with the display on card0. As expected /sys/class/drm/card0-HDMI-A-1/edid reports the EDID of my display.

When adjusting the Master volume slider in alsamixer, it also adjusts the PCM volume slider reported in sudo alsamixer, and vise-versa. The two should be in sync -- and they are.

HOWEVER, subsequent boots are different. The display switches to card1. ls /sys/class/drm/ reports...

card0  card1  card1-HDMI-A-1  card1-Writeback-1  renderD128  version

... with the display on card1.

The UI displays fine, and everything else on the system works fine except the following: When adjusting the Master volume slider in alsamixer, the PCM volume slider reported in sudo alsamixer does not change, and that causes a problem for my use case.

/boot/config.txt

# LCD display settings
hdmi_group=2
hdmi_mode=87
hdmi_cvt 800 480 60 6 0 0 0

# Enable the I2C port
dtparam=i2c_arm=on

# RTC
dtoverlay=i2c-rtc,ds3231

# Serial ports
enable_uart=1
core_freq=250
dtoverlay=uart1,txd1_pin=32,rxd1_pin=33

# Audio
dtparam=audio=on
dtoverlay=audremap,pins_40_41

# Enable DRM VC4 V3D driver
dtoverlay=vc4-kms-v3d,noaudio,cma-256

Steps to reproduce the behaviour

1. Create a new OS using Raspberry Pi imager
2. Boot it on the CM4S
3. Make note that ls /sys/class/drm reports the display on card0.
4. Note that when adjusting the Master volume slider in alsamixer, the PCM volume slider in sudo alsamixer also adjusts in synchronization.
5. Reboot the system
6. Make note that ls /sys/class/drm shows the display now on card1
7. Note that when adjusting the Master volume slider in alsamixer, the PCM volume slider in sudo alsamixer does not adjust in synchronization.

Device (s)

Raspberry Pi CM3+, Raspberry Pi CM3+ Lite, Raspberry Pi CM4, Raspberry Pi CM4 Lite, Other

System

Mar 21 2023 17:18:16
Copyright (c) 2012 Broadcom
version 3cc1c2dfc5460da9e1a0a4f48b48ab508c48bfe5 (clean) (release) (start)

Linux raspberrypi 6.1.21-v8+ #1639 SMP PREEMPT

Please note I'm using a pre-release kernel due to #5390, but the problem also exists in the 5.15 kernels.

Logs

No response

Additional context

The OS is created using a slightly modified pi-gen and, with the exception of the config.txt file, is identical for all Compute Module variants tested.

[JinShil]

I'm having trouble reproducing the issue on the CM4S's first boot where the display appears on card0. Now the display is always appearing on card1 despite whether it's the first boot or not.

What determines whether the display appears on card0 or card1?

[6by9]

What determines whether the display appears on card0 or card1?

Probe order during boot.
v3d has very few dependencies so can generally probe first.
vc4 has quite a few (reset controllers, I2C controllers, etc), so typically ends up with one or more defers before it can fully probe.

[JinShil]

Assuming the CM4S is mounted in a carrier board originally designed for the CM3+, where should the display end up? card0 like that of the CM3+, or card1 due to its lineage with the CM4?

Is there any difference between card0 and card1 on the CM4S?

Why is the Master volume in sync with the PCM volume when the display is on card0, but out of sync when the display is on card1?

[JinShil]

I figured out how to reproduce the issue more reliably. Removing the i2c and RTC lines from config.txt will sometimes put the display on card0. When they are added back, the display appears on card1:

/boot/config.txt

# display on card0
#dtparam=i2c_arm=on
#dtoverlay=i2c-rtc,ds3231

# display on card1
dtparam=i2c_arm=on
dtoverlay=i2c-rtc,ds3231

This behavior does not happen on the CM4. On the CM4, despite whether the i2c and RTC configurations appear in config.txt or not, the display is always on card1.

Still hoping for answers to the following questions:

1. Is there any difference between card0 and card1 on the CM4S?
2. Why is the Master volume in sync with the PCM volume when the display is on card0, but out of sync when the display is on card1?

[JinShil]

Now I can no longer reproduce the audio issue even when the display is on card1. This issue has me questioning my sanity. I'm closing it before it possesses someone else. If I stop hallucinating, I'll create a new issue hopefully with some connection to reality.

[JinShil]

I'm able to resolve the audio issue by adding this line to /etc/pulse/default.pa

load-module module-alsa-card device_id="0" name="platform-bcm2835_audio" card_name="alsa_card.platform-bcm2835_audio" namereg_fail=false tsched=no fixed_latency_range=no ignore_dB=no deferred_volume=yes use_ucm=yes avoid_resampling=no card_properties="module-udev-detect.discovered=1"

But, I don't know why that is required on the CM4S, but not on other compute modules.