From: Minxi Hou <houminxi@gmail.com>
To: jwollrath@web.de
Cc: amd-gfx@lists.freedesktop.org, Minxi Hou <houminxi@gmail.com>
Subject: Re: 7.0-rc4 dcn31_program_compbuf_size trace
Date: Mon, 18 May 2026 16:08:35 +0800 [thread overview]
Message-ID: <20260518080835.100682-1-houminxi@gmail.com> (raw)
In-Reply-To: <20260316094232.6bb6f0bf@schienar>
On Mon, 16 Mar 2026 09:42:32 +0100, Julian Wollrath wrote:
> when turning the display off via 'xset dpms force off' I observe the
> following warning and trace under 7.0-rc4 with a AMD Ryzen 7 PRO 8840U
I can reproduce the same warning on different hardware with a different
trigger.
Machine: HP Z66 G6 14 (ProBook 4 G1ah), AMD Ryzen 7 H 255 (HawkPoint1),
kernel 7.0.8-200.fc44.x86_64.
Trigger: HDMI hotplug with an external 4K monitor. The Z66's HDMI port
uses a DP-to-HDMI protocol converter with FRL support (dmesg shows
"DP-HDMI FRL PCON supported"). Connecting the monitor at boot causes
the first timeout during initialization; subsequent hotplug events
repeat it at runtime.
The call trace matches yours exactly:
dcn31_program_compbuf_size line:141
dcn20_optimize_bandwidth
dc_commit_state_no_check
dc_commit_streams
amdgpu_dm_atomic_commit_tail
Not seen with 6.19.x. CachyOS community bisected this to:
commit 592c5b80110d5e9e50873b5364818cb6f401e26d
"drm/amd/display: Migrate HUBBUB register access from hwseq to hubbub component"
One thing I noticed on my setup: the amdgpu driver defaults to
max_bpc=16 for the HDMI connector. With a HDMI 2.0 monitor (BenQ
EL2870U, Max TMDS 340 MHz) at 4K@60Hz, the higher color depth
increases bandwidth demand during compbuf reprogramming and makes the
timeout happen more often. Adding amdgpu.deep_color=0 helps but does
not fix the root cause.
Partial workaround:
amdgpu.runpm=0 amdgpu.gfx_off=0 amdgpu.deep_color=0
A patch proposed by Giuseppe Ranieri in the CachyOS issue tracker [1]
changes the REG_WAIT parameters from 1us*100 to 1000us*30 and resolves
the warning for several users with DCN 3.1 hardware. Discussion there
is ongoing about whether 2-10us*1000 would be a better fit.
[1] https://github.com/CachyOS/linux-cachyos/issues/810
Minxi Hou
next prev parent reply other threads:[~2026-05-18 13:01 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-16 8:42 7.0-rc4 dcn31_program_compbuf_size trace Julian Wollrath
2026-04-19 11:24 ` Eric Naim
2026-05-18 8:08 ` Minxi Hou [this message]
2026-05-20 8:58 ` Thorsten Leemhuis
2026-05-20 22:51 ` Deucher, Alexander
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