Black screen when modesetting with Core i7-620M

Upon booting Gentoo, my Thinkpad x201 with Core i7-620M integrated graphics displays initial kernel logs in low resolution, and then the screen goes black. Boot continues though, and I can log in blind via the console, or connect over SSH. If I set nomodeset the low-resolution display remains and I can boot and login normally via the console.

This is reproduced in the Gentoo 6.6 and 6.9 distribution kernels, linux-stable 6.3-rc1, and drm-tip. The Gentoo 6.1 distribution kernel, linux-stable v6.2, and an identically-configured Gentoo 6.6 distribution kernel on a Thinkpad x61 (Core 2 Duo T8100) all work as expected, with the screen successfully switching over to a high-resolution console after momentarily blacking out. I was able to bisect the regression to this commit.

git-bisect-log

dmesg

gord@x201 ~ $ uname -a
Linux x201 6.10.0-rc6-g451dfb0fe5a5 #1 SMP PREEMPT_DYNAMIC Sat Jul  6 12:20:52 PDT 2024 x86_64 Intel(R) Core(TM) i7 CPU M 620 @ 2.67GHz GenuineIntel GNU/Linux

gord@x201 ~ $ lspci -vnn -d :*:0300
00:02.0 VGA compatible controller [0300]: Intel Corporation Core Processor Integrated Graphics Controller [8086:0046] (rev 02) (prog-if 00 [VGA controller])
	Subsystem: Lenovo Device [17aa:215a]
	Flags: bus master, fast devsel, latency 0, IRQ 24
	Memory at f2000000 (64-bit, non-prefetchable) [size=4M]
	Memory at d0000000 (64-bit, prefetchable) [size=256M]
	I/O ports at 1800 [size=8]
	Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
	Capabilities: <access denied>
	Kernel driver in use: i915

Additional debugging discussion: https://forums.gentoo.org/viewtopic-t-1169102-postdays-0-postorder-asc-start-0.html