You have been subscribed to a public bug:

The i915 driver in the Linux kernel misrepresents the max output of
certain, newer, GPUs.

The output should be 16384x16384 for newer models (on at least 7th and
8th gen Intel CPUs) but it is stuck in 8192x8192.

The problem lies in:
https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/i915/intel_display.c

The conditional branch which is wrong is:

/* maximum framebuffer dimensions */
if (IS_GEN2(dev_priv)) {
        dev->mode_config.max_width = 2048;
        dev->mode_config.max_height = 2048;
} else if (IS_GEN3(dev_priv)) {
        dev->mode_config.max_width = 4096;
        dev->mode_config.max_height = 4096;
} else {
        dev->mode_config.max_width = 8192;
        dev->mode_config.max_height = 8192;
}

While I'm not certain which generations specifically allows the higher
output it is most certainly true of all iGPUs on the 7th and 8th
generation CPUs.

This is corroborated by Intel's own hardware pages, and can be proven by
running Wayland which ignores the limitation in the driver.

Bug is present both on all Ubuntu releases, including 18.04.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Xorg cannot exceed pipeline dimensions reported by kernel
https://bugs.launchpad.net/bugs/1790390
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