[Solved] kernel upgrade causing external monitor issues?

[GNUser]

(Note: This is quite off-topic since the machine in question runs Arch Linux, not TCL. That being said, the question has to do with the Linux kernel and not with Arch Linux specifically. I haven't frequented the Arch Linux kernel since 2015, so I thought I'd ask my kernel-related question to my TCL friends here.)

I have an old T500 laptop that functions as a digital media player. It runs Arch Linux and hasn't been updated since 2015 (the machine uses a local snapshot of the Arch Linux repo as it was back in 2015). Some relevant details: Linux kernel 4.1.x, i915 kernel module, Xorg, MATE desktop. Laptop is connected to a plasma TV using VGA cable. The output resolution (according to mate-display-properties) is 1600x900, 60 Hz. In  mate-display-properties  the option to "mirror" the laptop screen to the external monitor is selected. Everything works perfectly.

I decided on a whim to compile a new Linux kernel for said laptop, chose version 5.4.51 so that it was in the same 5.4.x series that I'm running in my personal TC11 daily driver. I installed the new kernel modules and kernel, created new initramfs. I changed nothing else on the laptop except pointing grub.cfg to the new kernel and initramfs. The laptop boots, graphics work perfectly on the laptop screen, all applications work.

Strangely, the only thing that's not working well is the video output on the TV: Some of the video on the left side is cut off. This happens even while the machine is booting and kernel chit-chat is scrolling past, so problem seems to have nothing to do with Xorg or MATE (which haven't changed, anyway). Problem must be caused by either the kernel itself or its i915 module. I checked in  mate-display-properties  and the settings are the same as before (1600x900, 60 Hz, "mirror" laptop's screen onto the external display).

Please, does anyone know of a kernel or i915 setting that can be changed so that the laptop's video output is centered on my TV, as it was when the laptop was running kernel 4.1.x?

[GNUser]

P.S. TV's "video mode" is 16:9, which was working fine when laptop had the old kernel.
I read somewhere that changing TV's video mode to "Just Scan" sometimes solves this kind of problem, but that option is grayed-out--I think "Just Scan" is only an option when TV is receiving a high-definition signal.

[GNUser]

I figured it out:

1. Open  mate-display-properties  and uncheck "mirror". Disable laptop's display so that only the external display (plasma TV) is enabled.

2. Now  mate-display-properties  allows me to increase the resolution to beyond what laptop's display can handle. I chose 1920 x 1080

3. Now TV allows me to chose "Just Scan" video mode, and problem goes away.

Thread can be marked as solved.

P.S. I don't see what any of this has to do with the kernel and/or the i915 module, but it obviously does. If anyone knows what the connection is, please share because I'd like to learn.

[Rich]

Hi GNUser

... Thread can be marked as solved. ...

Done.