drm/i915: Sanitize watermarks after hardware state readout (v4)

Although we can do a good job of reading out hardware state, the
graphics firmware may have programmed the watermarks in a creative way
that doesn't match how i915 would have chosen to program them.  We
shouldn't trust the firmware's watermark programming, but should rather
re-calculate how we think WM's should be programmed and then shove those
values into the hardware.

We can do this pretty easily by creating a dummy top-level state,
running it through the check process to calculate all the values, and
then just programming the watermarks for each CRTC.

v2:  Move watermark sanitization after our BIOS fb reconstruction; the
     watermark calculations that we do here need to look at pstate->fb,
     which isn't setup yet in intel_modeset_setup_hw_state(), even
     though we have an enabled & visible plane.

v3:
 - Don't move 'active = optimal' watermark assignment; we just undo
   that change in the next patch anyway.  (Ville)
 - Move atomic helper locking fix to separate patch.  (Maarten)

v4:
 - Grab connection_mutex before calling atomic helper to duplicate
   state.  The connector loop inside the helper will throw a WARN
   if we don't hold something to protect the connector list (and the
   helper itself doesn't try to lock the list).
 - Make failure to calculate watermarks for inherited state a WARN()
   since it probably indicates a serious problem in either our state
   readout code or our watermark code for this platform.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c1a3969f3d4c..043adfa65203 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -15276,6 +15276,78 @@ void intel_modeset_init_hw(struct drm_device *dev)
 	intel_enable_gt_powersave(dev);
 }
 
+/*
+ * Calculate what we think the watermarks should be for the state we've read
+ * out of the hardware and then immediately program those watermarks so that
+ * we ensure the hardware settings match our internal state.
+ *
+ * We can calculate what we think WM's should be by creating a duplicate of the
+ * current state (which was constructed during hardware readout) and running it
+ * through the atomic check code to calculate new watermark values in the
+ * state object.
+ */
+static void sanitize_watermarks(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	struct drm_atomic_state *state;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *cstate;
+	struct drm_modeset_acquire_ctx ctx;
+	int ret;
+	int i;
+
+	/* Only supported on platforms that use atomic watermark design */
+	if (!dev_priv->display.program_watermarks)
+		return;
+
+	/*
+	 * We need to hold connection_mutex before calling duplicate_state so
+	 * that the connector loop is protected.
+	 */
+	drm_modeset_acquire_init(&ctx, 0);
+retry:
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+	if (ret == -EDEADLK) {
+		drm_modeset_backoff(&ctx);
+		goto retry;
+	} else if (WARN_ON(ret)) {
+		return;
+	}
+
+	state = drm_atomic_helper_duplicate_state(dev, &ctx);
+	if (WARN_ON(IS_ERR(state)))
+		return;
+
+	ret = intel_atomic_check(dev, state);
+	if (ret) {
+		/*
+		 * If we fail here, it means that the hardware appears to be
+		 * programmed in a way that shouldn't be possible, given our
+		 * understanding of watermark requirements.  This might mean a
+		 * mistake in the hardware readout code or a mistake in the
+		 * watermark calculations for a given platform.  Raise a WARN
+		 * so that this is noticeable.
+		 *
+		 * If this actually happens, we'll have to just leave the
+		 * BIOS-programmed watermarks untouched and hope for the best.
+		 */
+		WARN(true, "Could not determine valid watermarks for inherited state\n");
+		return;
+	}
+
+	/* Write calculated watermark values back */
+	to_i915(dev)->wm.config = to_intel_atomic_state(state)->wm_config;
+	for_each_crtc_in_state(state, crtc, cstate, i) {
+		struct intel_crtc_state *cs = to_intel_crtc_state(cstate);
+
+		dev_priv->display.program_watermarks(cs);
+	}
+
+	drm_atomic_state_free(state);
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+}
+
 void intel_modeset_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -15396,6 +15468,13 @@ void intel_modeset_init(struct drm_device *dev)
 		 */
 		intel_find_initial_plane_obj(crtc, &plane_config);
 	}
+
+	/*
+	 * Make sure hardware watermarks really match the state we read out.
+	 * Note that we need to do this after reconstructing the BIOS fb's
+	 * since the watermark calculation done here will use pstate->fb.
+	 */
+	sanitize_watermarks(dev);
 }
 
 static void intel_enable_pipe_a(struct drm_device *dev)