Bug 110799

I enabled PSR on my Thinkpad T450s (Broadwell) with Linux 5.1.5. This works fine under X, but I get no screen updates on the fbcon (typing etc. does show no change on screen, only switching to/back X makes the stuff visible).
Without PSR, the fbcon works fine.

I investigated a bit and identified this code in drm/i915/intel_psr.c
(printk added by me) to exit PSR on fbcon dirty calls:

  /* By definition flush = invalidate + flush */
  if (frontbuffer_bits) {
    /*
     * Display WA #0884: all
     * This documented WA for bxt can be safely applied
     * broadly so we can force HW tracking to exit PSR
     * instead of disabling and re-enabling.
     * Workaround tells us to write 0 to CUR_SURFLIVE_A,
     * but it makes more sense write to the current active
     * pipe.
     */
    printk(KERN_DEBUG "WA\n");
    I915_WRITE(CURSURFLIVE(dev_priv->psr.pipe), 0);
  }

The code is called for fbcon changes, but as stated, it does not seem to have
the effect of exiting PSR on my hardware.