[Bug 96473] i915.ko corrupt text lines at top, [drm] GPU HANG: ecode 2:0:0x037fffc1, reason: Ring hung

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96473

--- Comment #14 from Taketo Kabe <fdporg at vega.pgw.jp> ---
Created attachment 124540
  --> https://bugs.freedesktop.org/attachment.cgi?id=124540&action=edit
dmesg, drm.debug=6

Better (or worse) solution:
Hardcode that first 1MB of stolen memory is really reserved in 865G.

diff -p -U6 ./drivers/gpu/drm/i915/i915_gem_stolen.c.ville
./drivers/gpu/drm/i915/i915_gem_stolen.c
--- ./drivers/gpu/drm/i915/i915_gem_stolen.c.ville      2016-06-08
10:23:53.000000000 +0900
+++ ./drivers/gpu/drm/i915/i915_gem_stolen.c    2016-06-15 14:59:55.000000000
+0900
@@ -116,12 +116,13 @@ static unsigned long i915_stolen_to_phys
                 * one to be allocated by the BIOS?
                 */
                pci_bus_read_config_word(dev->pdev->bus, PCI_DEVFN(0, 0),
                                         I865_TOUD, &toud);

                base = toud << 16;
+               base += 1024 * 1024; /* FIXME assume first 1MB is really
reserved */
        } else if (IS_I85X(dev)) {
                u32 tseg_size = 0;
                u32 tom;
                u8 tmp;

                pci_bus_read_config_byte(dev->pdev->bus, PCI_DEVFN(0, 0),


This also works on real machine. No text corruption, no GPU HANG.


After these,
I'm beginning to think that Comment 13 fix is nontheless right, because
- I865_TOUD is in "Reserved" region of 865G's PCI config registers.
  Depending on it is wrong, even if it holds sane value in practice.
- It looks like reserved memory is really reserved and not reusable for
/dev/fb0 .
  VGA BIOS et al is sitting there.

Ville Syrjala in https://patchwork.kernel.org/patch/3448921/
claimed that 865G is bit different and needs verify on a real system.
Maybe noone had tested on real system since.

865G is a decade-old chipset; for enterprise level, so maybe not worth effort 
to claim panic-proof /dev/fb0 region.
For others, "it works" is important and Comment 13 fix is enough.
Any thoughts?

The reason I'm sticking to this problem is that I use CentOS 6
on 865G machine, and upstream RHEL6.8 started retrofitting
kernel 4.4 drivers/gpu/drm/ code onto kernel 2.6.32 (amazing!).

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