[Bug 109248] [WHL] FIFO underruns on a hybrid machine but only while on "performance" (dGPU) mode

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109248

--- Comment #7 from Cooper Chiou <cooper.chiou at intel.com> ---
Canonical has identified this i915 patch which can't reproduce issue on kernel
4.20 by watermark/ddb fix but it's difficult to apply to kernel 4.15 since lots
of commit dependence and conflicts.

commit ff43bc379e16c9195323cb88ac0c9f4d0613d07a (refs/bisect/bad)
Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
Date: Tue Nov 27 18:59:00 2018 +0200

    drm/i915: Move ddb/wm programming into plane update/disable hooks on skl+

    On SKL+ the plane WM/BUF_CFG registers are a proper part of each
    plane's register set. That means accessing them will cancel any
    pending plane update, and we would need a PLANE_SURF register write
    to arm the wm/ddb change as well.

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