drm/i915: Track whether an atomic transaction changes the active CRTC's

For the purposes of DDB re-allocation we need to know whether a
transaction changes the list of CRTC's that are active.  While
state->modeset could be used for this purpose, that would be slightly
too aggressive since it would lead us to re-allocate the DDB when a
CRTC's mode changes, but not its final active state.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463061971-19638-7-git-send-email-matthew.d.roper@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -13270,6 +13270,9 @@ static int intel_modeset_checks(struct drm_atomic_state *state)
 			intel_state->active_crtcs |= 1 << i;
 		else
 			intel_state->active_crtcs &= ~(1 << i);
+
+		if (crtc_state->active != crtc->state->active)
+			intel_state->active_pipe_changes |= drm_crtc_mask(crtc);
 	}
 
 	/*

drivers/gpu/drm/i915/intel_drv.h

@@ -291,6 +291,16 @@ struct intel_atomic_state {
 
 	bool dpll_set, modeset;
 
+	/*
+	 * Does this transaction change the pipes that are active?  This mask
+	 * tracks which CRTC's have changed their active state at the end of
+	 * the transaction (not counting the temporary disable during modesets).
+	 * This mask should only be non-zero when intel_state->modeset is true,
+	 * but the converse is not necessarily true; simply changing a mode may
+	 * not flip the final active status of any CRTC's
+	 */
+	unsigned int active_pipe_changes;
+
 	unsigned int active_crtcs;
 	unsigned int min_pixclk[I915_MAX_PIPES];