[Intel-gfx] [PATCH v6 2/2] drm/i915: Make sure we have enough memory bandwidth on ICL

[Ville Syrjälä]

On Fri, May 24, 2019 at 06:36:14PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> 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>

Series pushed to dinq. Thanks for the reviews.

-- 
Ville Syrjälä
Intel