[Bug 110838] Black screen at desktop on kernel for ICL only

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110838

Mark Janes <mark.a.janes at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |bisected
           Assignee|intel-gfx-bugs at lists.freede |ville.syrjala at linux.intel.c
                   |sktop.org                   |om
             Status|NEEDINFO                    |ASSIGNED

--- Comment #8 from Mark Janes <mark.a.janes at intel.com> ---
Bisected to:

Author:     Ville Syrjälä <ville.syrjala at linux.intel.com>
drm/i915: Make sure we have enough memory bandwidth on ICL

ICL has so many planes that it can easily exceed the maximum
effective memory bandwidth of the system. We must therefore check
that we don't exceed that limit

The algorithm is very magic number heavy and lacks sufficient
explanation for now. We also have no sane way to query the
memory clock and timings, so we must rely on a combination of
raw readout from the memory controller and hardcoded assumptions
The memory controller values obviously change as the system
jumps between the different SAGV points, so we try to stabilize
it first by disabling SAGV for the duration of the readout

The utilized bandwidth is tracked via a device wide atomic
private object. That is actually not robust because we can't
afford to enforce strict global ordering between the pipes
Thus I think I'll need to change this to simply chop up the
available bandwidth between all the active pipes. Each pipe
can then do whatever it wants as long as it doesn't exceed
its budget. That scheme will also require that we assume that
any number of planes could be active at any time

TODO: make it robust and deal with all the open questions

v2: Sleep longer after disabling SAGV
v3: Poll for the dclk to get raised (seen it take 250ms
    If the system has 2133MT/s memory then we pointlessly
    wait one full second
v4: Use the new pcode interface to get the qgv points rather
    that using hardcoded numbers
v5: Move the pcode stuff into intel_bw.c (Matt)
    s/intel_sagv_info/intel_qgv_info/
    Do the NV12/P010 as per spec for now (Matt)
    s/IS_ICELAKE/IS_GEN11/
v6: Ignore bandwidth limits if the pcode query fails

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>                    
Reviewed-by: Matt Roper <matthew.d.roper at intel.com>
Acked-by: Clint Taylor <Clinton.A.Taylor at intel.com>
Link:
https://patchwork.freedesktop.org/patch/msgid/20190524153614.32410-1-ville.syrjala@linux.intel.com

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