linux-kernel - [REGRESSION] HDMI monitor not working on Radxa Rock 5B after phy rockchip samsung hdptx HDMI 2.1 FRL patchset

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Message-ID: <b32164001947ba922aefb6ca86a8dc59e9323d2b.camel@online.de>
Date: Wed, 11 Feb 2026 22:20:38 +0100
From: Thomas Niederprüm <dubito@...ine.de>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>, Vinod Koul	
 <vkoul@...nel.org>, Neil Armstrong <neil.armstrong@...aro.org>, Heiko
 Stuebner	 <heiko@...ech.de>, linux-phy@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, regressions@...ts.linux.dev
Subject: [REGRESSION] HDMI monitor not working on Radxa Rock 5B after phy
 rockchip samsung hdptx HDMI 2.1 FRL patchset

Hi,

I'm running a Radxa Rock 5B (rk3588) on a 10+ year old Samsung TV screen
connected via HDMI. This worked flawlessly in 6.18.7 but does not work on linux-
next. I bisected the problem and identified commit 3481fc04 to be the first bad
commit. This points to the phy PLL clock rate calculation to be the problem in
connection with my monitor. As it seems relevant, I attached the EDID of my
monitor.

I'm booting the kernel out of EDK2 after which efifb is correctly taking over
the initialized display and I can see the initial kernel boot messages on the
HDMI output. After the drm/kms in the kernel takes over the screen shortly turns
black, changes resolution, and then correctly displays on 6.18.7. However, in
linux-next the screen remains black after kms took over. I cannot see any
obvious differences in the boot logs but I attached two boot logs, one for the
working 6.18.7 kernel and one for the non-working linux-next kernel.

When reverting 3481fc04..de5dba83 (i.e. the faulty commit and the ones that
followed in the HDMI 2.1 FRL series) I can build a working kernel from linux-
next.

I don't know where to dig from here but I'm happy to run any test necessary to
track down the problem.

Best regards,

Thomas Niederprüm

#regzbot introduced:  3481fc04d969bc1528c2d1f7c02443a9fccf1a83

Download attachment "edid.bin" of type "application/octet-stream" (256 bytes)

View attachment "boot.non-working" of type "text/plain" (69369 bytes)

View attachment "boot.working" of type "text/plain" (77223 bytes)