[Bug 72864] [HSW ULT/BDW]igt/kms_cursor_crc fails with eDP

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=72864

--- Comment #19 from lu hua <huax.lu at intel.com> ---
Created attachment 107757
  --> https://bugs.freedesktop.org/attachment.cgi?id=107757&action=edit
output

(In reply to Paulo Zanoni from comment #18)
> Ok, so I did some more investigation... The problem only appears to happen
> on pipe A. Arthur suggested that some package C state may be interfering
> with memory/caches, and the HW is calculating CRC the result based on a
> wrong input.
> 
> So I did some test, and if we keep the i915_forcewake_user file open, the
> problem _does not_ happen.
> 
> The easiest way I found to test this is:
> 
> - open a terminal
> - become root
> - run "irb"
> - on its prompt, type: "a =
> File.open("/sys/kernel/debug/dri/0/i915_forcewake_user")"
> - leave this terminal as it is
> - open a new terminal
> - run sudo ./kms_cursor_crc
> 
> The test will succeed!
> 
> For the real fix, I guess we have to find a way to prevent deep PC states
> whenever we're calculating CRCs for pipe A...


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