drm/i915: fix screen flickering

Commit c9f038a1a592 ("drm/i915: Don't assume primary & cursor are
always on for wm calculation (v4)") fixes a null pointer dereference.
Setting the primary and cursor panes to false in
ilk_compute_wm_parameters to false does however give the following
errors in the kernel log and causes the screen to flicker.

[  101.133716] [drm:intel_set_cpu_fifo_underrun_reporting [i915]]
*ERROR* uncleared fifo underrun on pipe A
[  101.133725] [drm:intel_cpu_fifo_underrun_irq_handler [i915]]
*ERROR* CPU pipe A FIFO underrun

Always setting the panes to enabled fixes this error.

Helped-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 11 insertions, 13 deletions

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index fa4ccb346389..555b896d2bda 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2045,22 +2045,20 @@ static void ilk_compute_wm_parameters(struct drm_crtc *crtc,
         p->pipe_htotal = intel_crtc->config->base.adjusted_mode.crtc_htotal;
         p->pixel_rate = ilk_pipe_pixel_rate(dev, crtc);
 
-        if (crtc->primary->state->fb) {
-                p->pri.enabled = true;
+        if (crtc->primary->state->fb)
                 p->pri.bytes_per_pixel =
                         crtc->primary->state->fb->bits_per_pixel / 8;
-        } else {
-                p->pri.enabled = false;
-                p->pri.bytes_per_pixel = 0;
-        }
+        else
+                p->pri.bytes_per_pixel = 4;
+
+        p->cur.bytes_per_pixel = 4;
+        /*
+         * TODO: for now, assume primary and cursor planes are always enabled.
+         * Setting them to false makes the screen flicker.
+         */
+        p->pri.enabled = true;
+        p->cur.enabled = true;
 
-        if (crtc->cursor->state->fb) {
-                p->cur.enabled = true;
-                p->cur.bytes_per_pixel = 4;
-        } else {
-                p->cur.enabled = false;
-                p->cur.bytes_per_pixel = 0;
-        }
         p->pri.horiz_pixels = intel_crtc->config->pipe_src_w;
         p->cur.horiz_pixels = intel_crtc->base.cursor->state->crtc_w;