• Ville Syrjälä's avatar
    drm/i915: Make sure we have enough memory bandwidth on ICL · c457d9cf
    Ville Syrjälä authored
    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: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
    Reviewed-by: default avatarMatt Roper <matthew.d.roper@intel.com>
    Acked-by: default avatarClint Taylor <Clinton.A.Taylor@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20190524153614.32410-1-ville.syrjala@linux.intel.com
    c457d9cf
intel_bw.c 10 KB