[Bug 100457] [HSW] live_hangcheck - Failed to start request

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100457

--- Comment #5 from mwa <matthew.auld at intel.com> ---
Okay, so bisection pointed to:

commit e09a3036412a959689bacf017bf2cbc226c9fea4
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Tue Apr 11 11:13:39 2017 +0100

    drm/i915: Use __intel_uncore_wait_for_register_fw for sandybride_pcode_read

    Since the sandybridge_pcode_read() may be called from
    skl_pcode_request() inside an atomic context (with preempt disabled), we
    should avoid hitting any sleeping paths. Currently is being called with
    a 500ms timeout, irrespective of being inside an atomic context or not.
    This is reduced down to 500us to play nice with the atomic context, and
    that appears to be sufficient to keep BAT happy (we have a DRM_ERROR
    should it timeout), i.e. we do not see any 500us pcode timeouts for
    normal use. So leave it as a pure spin without having to introduce new
    code paths to separate atomic/normal contexts.

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