On maandag 8 februari 2021 15:00:26 CET Ryutaroh Matsumoto wrote:
> > With kernel version 5.10.9 (linux-image-5.10.0-2-arm64) it all seemed
> > fixed, but returned with 5.10.12 (linux-image-5.10.0-3-arm64) and is also
> > present with 5.10.13.
> 
> The difference in Debian kernel 5.10.9 was that vc4.ko was disabled by
> mistake. I guess that module_blacklist=vc4 in kernel command line
> suppresses the symptom.
> All other Debian kernel 5.10.x have vc4.ko enabled in arm64.

Indeed, you're correct! Thanks.
I haven't tried blacklisting it, but IIUC that means it doesn't work in 5.10 
with vc4 at all (on arm64 at least).

I've now setup another RPi3B+ ~ the same as my rpi-mpd, but / moved to a 
PiDrive and created 52Gi swap partition to build the upstream kernel (+config) 
and subsequently one with the requested patches.

diederik@rpi-mpd:~$ git diff /boot/config-5.10.0-2-arm64 /boot/config-5.10.0-3-
arm64
diff --git a/boot/config-5.10.0-2-arm64 b/boot/config-5.10.0-3-arm64
index 35d6f98..e8eafc9 100644
--- a/boot/config-5.10.0-2-arm64
+++ b/boot/config-5.10.0-3-arm64
@@ -1,6 +1,6 @@
 #
 # Automatically generated file; DO NOT EDIT.
-# Linux/arm64 5.10.9 Kernel Configuration
+# Linux/arm64 5.10.13 Kernel Configuration
 #
 CONFIG_CC_VERSION_TEXT="gcc-10 (Debian 10.2.1-6) 10.2.1 20210110"
 CONFIG_CC_IS_GCC=y
@@ -23,7 +23,7 @@ CONFIG_INIT_ENV_ARG_LIMIT=32
 # CONFIG_COMPILE_TEST is not set
 CONFIG_LOCALVERSION=""
 # CONFIG_LOCALVERSION_AUTO is not set
-CONFIG_BUILD_SALT="5.10.0-2-arm64"
+CONFIG_BUILD_SALT="5.10.0-3-arm64"
 CONFIG_DEFAULT_INIT=""
 CONFIG_DEFAULT_HOSTNAME="(none)"
 CONFIG_SWAP=y
@@ -737,7 +737,7 @@ CONFIG_CRYPTO_AES_ARM64_CE_BLK=m
 CONFIG_CRYPTO_AES_ARM64_NEON_BLK=m
 CONFIG_CRYPTO_CHACHA20_NEON=m
 CONFIG_CRYPTO_POLY1305_NEON=m
-# CONFIG_CRYPTO_NHPOLY1305_NEON is not set
+CONFIG_CRYPTO_NHPOLY1305_NEON=m
 CONFIG_CRYPTO_AES_ARM64_BS=m
 
 #
@@ -3339,7 +3339,7 @@ CONFIG_USB_IPHETH=m
 CONFIG_USB_SIERRA_NET=m
 CONFIG_USB_VL600=m
 CONFIG_USB_NET_CH9200=m
-# CONFIG_USB_NET_AQC111 is not set
+CONFIG_USB_NET_AQC111=m
 CONFIG_WLAN=y
 # CONFIG_WIRELESS_WDS is not set
 CONFIG_WLAN_VENDOR_ADMTEK=y
@@ -5937,7 +5937,6 @@ CONFIG_DRM_AMDGPU_USERPTR=y
 # Display Engine Configuration
 #
 CONFIG_DRM_AMD_DC=y
-CONFIG_DRM_AMD_DC_DCN=y
 CONFIG_DRM_AMD_DC_HDCP=y
 CONFIG_DRM_AMD_DC_SI=y
 # end of Display Engine Configuration
@@ -6097,7 +6096,8 @@ CONFIG_DRM_DW_HDMI_I2S_AUDIO=m
 CONFIG_DRM_DW_MIPI_DSI=m
 # end of Display Interface Bridges
 
-# CONFIG_DRM_VC4 is not set
+CONFIG_DRM_VC4=m
+CONFIG_DRM_VC4_HDMI_CEC=y
 # CONFIG_DRM_ETNAVIV is not set
 # CONFIG_DRM_ARCPGU is not set
 CONFIG_DRM_HISI_HIBMC=m
@@ -9531,8 +9531,6 @@ CONFIG_CRYPTO_WP512=m
 #
 CONFIG_CRYPTO_AES=m
 CONFIG_CRYPTO_AES_TI=m
-CONFIG_CRYPTO_ANUBIS=m
-CONFIG_CRYPTO_ARC4=m
 CONFIG_CRYPTO_BLOWFISH=m
 CONFIG_CRYPTO_BLOWFISH_COMMON=m
 CONFIG_CRYPTO_CAMELLIA=m
@@ -9541,13 +9539,10 @@ CONFIG_CRYPTO_CAST5=m
 CONFIG_CRYPTO_CAST6=m
 CONFIG_CRYPTO_DES=m
 CONFIG_CRYPTO_FCRYPT=m
-CONFIG_CRYPTO_KHAZAD=m
 CONFIG_CRYPTO_SALSA20=m
 CONFIG_CRYPTO_CHACHA20=m
-CONFIG_CRYPTO_SEED=m
 CONFIG_CRYPTO_SERPENT=m
 # CONFIG_CRYPTO_SM4 is not set
-CONFIG_CRYPTO_TEA=m
 CONFIG_CRYPTO_TWOFISH=m
 CONFIG_CRYPTO_TWOFISH_COMMON=m
 
@@ -9577,7 +9572,7 @@ CONFIG_CRYPTO_USER_API_SKCIPHER=m
 CONFIG_CRYPTO_USER_API_RNG=m
 # CONFIG_CRYPTO_USER_API_RNG_CAVP is not set
 CONFIG_CRYPTO_USER_API_AEAD=m
-CONFIG_CRYPTO_USER_API_ENABLE_OBSOLETE=y
+# CONFIG_CRYPTO_USER_API_ENABLE_OBSOLETE is not set
 # CONFIG_CRYPTO_STATS is not set
 CONFIG_CRYPTO_HASH_INFO=y