On Fri, 10 Jan 2014, Cyrille Pontvieux cyrille@enialis.net wrote:

I recently acquired a Toshiba laptop with a Intel Graphics 4600M in it (8086:0416, subsystem 1179:fa82). This Toshiba system is provided with UEFI (EFI Insyde H2O 1.30). I compiled and use Linux kernel 3.13-rc7 (config.gz attached) This system is provided with Windows 8.1 OS and the gpu is working fine under it. If I boot the laptop and Linux in BIOS compatible mode, gpu is working ok. If I boot the laptop and Linux in UEFI, there is strange problems on pixels rendering, both in the console (framebuffer) and in Xorg. The problem is that the colors are not "right" depending on the position of the pixel on the screen. For example, on white-on-black text, the white text is never rendered white but with an alternance of red, green, blue (cyan ?) and magenta pixels. If you look far enough, it looks white. There also appear to have maybe one pixel shifting or bluring, hard to tell. I also attached a photo to better explain the problem.

The problem is exactly the same in framebuffer console or in Xorg. It appears early in the boot process. Before that the rendering is correct. Linux penguins are show correctly before a screen reset is done and the problem appears. I also attached the output of dmesg for that case.

If I boot by disabling KMS (with nomodeset), the rendering is ok in Linux console, but I cannot run Xorg: (EE) open /dev/dri/card0: No such file or directory (EE) VESA(0): V_BIOS address 0x0 out of range (EE) Screen(s) found, but none have a usable configuration. But maybe this is a separate problem and I need to compile newer intel Xorg drivers (mine is 2.21.15). I also attached the output of dmesg for that case.

I could provide more input, or compile a custom/patched kernel to help correcting the problem. One more thing: contrary to what occurs recently with some i915 driver users, my gpu never hangs.

This bug is tracked at https://bugzilla.kernel.org/show_bug.cgi?id=68651