drm/i915/dsb: Clear DSB_ENABLE_DEWAKE once the DSB is done

In order to avoid the DSB keeping the DEwake permanently
asserted we must clear DSB_PMCTRL_2.DSB_FORCE_DEWAKE once
we are done. For good measure do the same for
DSB_PMCTRL.DSB_ENABLE_DEWAKE.

Experimentally this doens't seem to be actually necessary
(unlike with DSB_FORCE_DEWAKE). That is, the DSB_ENABLE_DEWAKE
doesn't seem to do anything whenever the DSB is not active.
But I'd hate to waste a ton of power in case there I'm wrong
and there is some way DEwake could remaing asserted. One extra
register write is a small price to pay for some peace of mind.

Signed-off-by: Ville Syrjälä <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Animesh Manna <[email protected]>

drivers/gpu/drm/i915/display/intel_dsb.c

@@ -464,8 +464,10 @@ void intel_dsb_finish(struct intel_dsb *dsb)
 	/*
 	 * DSB_FORCE_DEWAKE remains active even after DSB is
 	 * disabled, so make sure to clear it (if set during
-	 * intel_dsb_commit()).
+	 * intel_dsb_commit()). And clear DSB_ENABLE_DEWAKE as
+	 * well for good measure.
 	 */
+	intel_dsb_reg_write(dsb, DSB_PMCTRL(crtc->pipe, dsb->id), 0);
 	intel_dsb_reg_write_masked(dsb, DSB_PMCTRL_2(crtc->pipe, dsb->id),
 				   DSB_FORCE_DEWAKE, 0);