Interestingly I have a similar experience of flashing displays, though my issue reflected the backlight and not the panel poweron sequence. After chip-level-flashing an Ivy Bridge Dell laptop with a corrupted BIOS chip, I was disappointed to find that the backlight was dimmed using PWM at 100 Hz (10ms periods) (CORRECTION: 200 Hz), where 50% brightness in Linux sets the light to turn on for 5ms, then off, and repeat every 10ms. This causes noticeable flicker when I move my hand in front of the screen.<p>Reading through the i915 driver and Sandy/Ivy Bridge GPU datasheets, I found that the backlight was controlled by two GPU registers at 0x48250 and 0x48254 (CPU-written?), with mirrors-ish at 0xC8250 and 0xC8254 (PCH-written?). There's actually a script to decrease the backlight period register at <a href="https://github.com/edio/intelpwm-udev" rel="nofollow">https://github.com/edio/intelpwm-udev</a>, but the problem is that Linux still scales the pulse width register based on the original period (10ms) at time of bootup and doesn't see the userspace tool writing a shorter period (higher frequency). If you halve the backlight period to 5ms, 50% brightness suddenly configures the GPU to turn the screen on for 5 of 5 ms, setting the screen to full brightness instead (all lower brightness values are doubled, and all higher ones are technically illegal chip configurations). As an added gotcha, if you write to the wrong register mirror (0xCxxxx vs 0x4xxxx), you get seizure-inducing screen backlight flicker comparable to the issue report at <a href="https://gitlab.freedesktop.org/drm/intel/-/issues/7013" rel="nofollow">https://gitlab.freedesktop.org/drm/intel/-/issues/7013</a>.<p>I tried recompiling the i915 driver to increase the PWM frequency at boot time, but was unable to compile and replace that driver alone due to symbol version mismatches (and I didn't want to rebuild the whole kernel on an obsolete dual-core Ivy Bridge). So I tried changing the backlight frequency in the BIOS itself, which was OS-agnostic and didn't require editing Linux drivers. I began decompiling the UEFI firmware in Ghidra and tracing control flow across multiple undocumented labyrinthine EFI executables, finding that I had to modify a VBT file's backlight PWM frequency field to change the refresh rate. Sadly this only affected pure UEFI boot and not CSM mode, but disabling CSM causes Windows 7 (the OS I used when the laptop was new, and which I keep this laptop just to run) to show a black screen. And I got burnt out from reversing EFI, <i>and</i> broke a flash chip leg and two motherboard pads reflashing my BIOS (and barely managed to patch the BIOS chip circuit back together with bodge wire soldered to the chip's stub)... so I'm still stuck with 100Hz flickering...