[Bug 47481] Random blank screen: radeon_cs_ib_chunk Failed to schedule IB on AMD PALM

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https://bugzilla.kernel.org/show_bug.cgi?id=47481





--- Comment #5 from Anisse Astier <anisse at astier.eu>  2012-09-17 17:41:33 ---
I did a first round of bisect:
375849ce878f1a2dfac12ea2a62b361ab6b7f9a5 is the first bad commit
commit 375849ce878f1a2dfac12ea2a62b361ab6b7f9a5
Author: Jerome Glisse <jglisse at redhat.com>
Date:   Fri Jul 27 16:32:24 2012 -0400

    drm/radeon: do not reenable crtc after moving vram start address

    commit 81ee8fb6b52ec69eeed37fe7943446af1dccecc5 upstream.

    It seems we can not update the crtc scanout address. After disabling
    crtc, update to base address do not take effect after crtc being
    reenable leading to at least frame being scanout from the old crtc
    base address. Disabling crtc display request lead to same behavior.

    So after changing the vram address if we don't keep crtc disabled
    we will have the GPU trying to read some random system memory address
    with some iommu this will broke the crtc engine and will lead to
    broken display and iommu error message.

    So to avoid this, disable crtc. For flicker less boot we will need
    to avoid moving the vram start address.

    This patch should also fix :

    https://bugs.freedesktop.org/show_bug.cgi?id=42373




Problem: I'm not sure this is in fact the culprit, and that this commit didn't
just uncover another bug. During the bisect between v3.5 and v3.5.3 I had
another problem: machine would some time block at boot with a black screen (no
backlight); I ignored it because it didn't have the same symptom (boot ok,
blank screen, backlight on, error on X start).

That's why I'm not sure if the bug isn't more ancient (between v3.2 and v3.5).

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