[coreboot - Bug #315] (New) Xorg/Wayland show black screen when system memory is 4GB or higher

Issue #315 has been reported by Master Geek.

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Bug #315: Xorg/Wayland show black screen when system memory is 4GB or higher
https://ticket.coreboot.org/issues/315

* Author: Master Geek
* Status: New
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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Board: ASROCK G41M-VS3 R2.0
CB Revision: coreboot-4.14-1258-gfbc46a3bfb

When this board has one memory stick with 2GB of ram, or two memory sticks with 1GB and 2GB (3GB total) there's no issue with display; Xorg and wayland (using weston) work as expected. But when there's 4GB or maybe more (two 2GB sticks only available, haven't tried a single 4GB stick) the system works as expected up to just before starting Xorg or wayland, the screen goes black and nothing else happens. Returning to a tty by means of Ctrl-Alt-# 'ing to some other tty doesn't bring display back, neither does exitting/killing Xorg or wayland. Not even forcefully removing and reloading the relevant kernel modules (i915, drm) does anything to bring the display back, display will only comeback with a reboot.

When the screen goes black there's no system freeze of any kind, and the kernel complains with a single line:
    "i915 0000:00:02.0: [drm] *ERROR* CPU pipe A FIFO underrun"
that isn't very helpful for debugging imo.

Attached dmesg loglevel=9 logs of stock bios, coreboot with 4GB (coreboot_bad) and with 2GB (coreboot_good), cbmem console log of coreboot with 2GB (cbmem_good).

---Files--------------------------------
cb_config.txt (16.3 KB)
cbmem_good.log (31.3 KB)
dmesg_coreboot_bad.log (443 KB)
dmesg_coreboot_good.log (457 KB)
dmesg_stock_bios.log (315 KB)