[fairydust] M2 Max: HDMI detects but no output, USB-C DP not working

[mwmetcalf1]

Hardware

• Model: MacBook Pro 16" M2 Max 2023 (j416c, t6021)
• Display: Sansui 3440x1440 ultrawide via native HDMI port

Kernel

• Branch: fairydust
• Version: 6.18.10-ARCH-FAIRYDUST+
• Build: Custom compiled from fairydust branch

Issue

Native HDMI port successfully detects display and DCP initializes at correct resolution, but display remains black (no output).

What works:

✅ Display detection via HDMI port
✅ DCP initialization
✅ Correct resolution detected (3440x1440@60Hz)
✅ DRM connector shows "connected"
✅ GNOME sees the display in settings

What doesn't work:

❌ No visual output on external display
❌ Display shows as "disabled" in DRM
❌ Same DPMS/power state issue as stable kernel

dmesg output

apple-dcp 289c00000.dcp: DP2HDMI HPD irq, connected:1
apple-dcp 289c00000.dcp: dcp_hotplug() connected:1 valid_mode:0 nr_modes:20
apple-dcp 289c00000.dcp: set_digital_out_mode(color:70 timing:41) "3440x1440": 60 321670 3440 3488 3520 3620 1440 1443 1448 1481
apple-dcp 289c00000.dcp: set_digital_out_mode finished:8271

DRM status

/sys/class/drm/card5-HDMI-A-1/status: connected
/sys/class/drm/card5-HDMI-A-1/enabled: disabled

USB-C DP Alt Mode

Also tested USB-C DisplayPort Alt Mode - not functional on M2 Max:

• Type-C ports detected (port0-3)
• No DisplayPort alternate modes advertised
• Display crossbar driver loaded but DP not available

Notes

This is the same behavior as stable kernel 6.18.10 - HDMI detection works but output fails. Falling back to DisplayLink which works reliably.

[JieningYu]

The config of your running kernel?

[mwmetcalf1]

here you go:

fairydust-m2max-config.txt

[JieningYu]

Have you tried the 'blessed' usbc port (or all) on you machine for dp-altmode, and for hdmi right after boot? The config seems no prob.

[mwmetcalf1]

I tested:

USB-C DP Alt Mode:

• Tried all 3 USB-C ports (ports 1, 2, 3)
• None advertised DisplayPort alternate modes
• supported_accessory_modes showed "none" for all ports
• Display crossbar driver loaded but no DP capability exposed

Native HDMI:

• Travel monitor (16" 2520x1680 IPS): ✅ Works! Display output successful via native HDMI
• Sansui ultrawide (34" 3440x1440): ❌ Display detected and initialized in dmesg, but no visual output
• Both cold boot and hot-plug tested on Sansui
• Sansui shows as "connected" but "disabled" in DRM
• GNOME sees the Sansui but can't enable it

The travel monitor worked fine via native HDMI, but the ultrawide fails despite DCP successfully detecting and initializing at 3440x1440@60Hz.

Would you like me to test any specific kernel parameters or configuration changes?

[mwmetcalf1]

i update the fairydust branch to test again, this time i got this:

WARNING: CPU: 6 PID: 273 at drivers/phy/apple/atc.c:2145 atcphy_mux_set+0xec8/0xfc4 [phy_apple_atc]
Call trace:
 atcphy_mux_set+0xec8/0xfc4 [phy_apple_atc]
 typec_mux_set+0x60/0xa0 [typec]
 cd321x_update_work+0x474/0x860 [tps6598x]

This occurs when switching USB-C ports or attempting DP Alt Mode. The PHY driver (atcphy_mux_set) hits an unexpected state and can't configure the hardware properly.

This explains why supported_accessory_modes shows "none" - the driver knows it can't set up DP Alt Mode on M2 Max.

Native HDMI continues to show the same power state issue as originally reported.

[vrutkovs]

Also happens on my M2 Mini Pro - tested that it happens on e984fa6 (asahi-wip) too

[vrutkovs]

This seems to work here when I switch to b0b5bbf