[Bug 198745] Blank screen on RX 580 with AMDGPU Display Core enabled

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=198745

--- Comment #17 from Harry Wentland (harry.wentland@amd.com) ---
Thanks for checking. Non-DC display driver and DC do detection somewhat
differently. It's somewhat difficult to say what's going wrong there.

Do you see different behavior when booting headless, then plugging in the
display?

If you're interested in debugging I'd probably use ftrace to get started,
checking that the functions get hit:
- handle_hpd_irq (only on hotplug)
- dc_link_detect (crucial to detection)
- dc_sink_create
- dm_helpers_read_local_edid
- drm_get_edid
- dm_helpers_parse_edid_caps
- amdgpu_dm_update_connector_after_detect
- drm_mode_connector_update_edid_property

Script to do ftrace debugging (run as root):

#!/bin/bash
cd /sys/kernel/debug/tracing/

echo handle_hpd_irq >> set_ftrace_filter
echo dc_link_detect >> set_ftrace_filter
echo dc_sink_create >> set_ftrace_filter
echo dm_helpers_read_local_edid >> set_ftrace_filter
echo drm_get_edid >> set_ftrace_filter
echo dm_helpers_parse_edid_caps >> set_ftrace_filter
echo amdgpu_dm_update_connector_after_detect >> set_ftrace_filter
echo drm_mode_connector_update_edid_property >> set_ftrace_filter

echo function_graph >> current_tracer
echo '' >> trace
cat trace_pipe

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