drm/i915/dsb: Add support for non-posted DSB registers writes

Writing specific transcoder registers (and as it turns out, the
legacy LUT as well) via DSB needs a magic sequence to emit
non-posted register writes. Add a helper for this.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230606191504.18099-11-ville.syrjala@linux.intel.comReviewed-by: Uma Shankar <uma.shankar@intel.com>

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

@@ -261,6 +261,26 @@ void intel_dsb_noop(struct intel_dsb *dsb, int count)
 			       DSB_OPCODE_NOOP << DSB_OPCODE_SHIFT);
 }
 
+void intel_dsb_nonpost_start(struct intel_dsb *dsb)
+{
+	struct intel_crtc *crtc = dsb->crtc;
+	enum pipe pipe = crtc->pipe;
+
+	intel_dsb_reg_write_masked(dsb, DSB_CTRL(pipe, dsb->id),
+				   DSB_NON_POSTED, DSB_NON_POSTED);
+	intel_dsb_noop(dsb, 4);
+}
+
+void intel_dsb_nonpost_end(struct intel_dsb *dsb)
+{
+	struct intel_crtc *crtc = dsb->crtc;
+	enum pipe pipe = crtc->pipe;
+
+	intel_dsb_reg_write_masked(dsb, DSB_CTRL(pipe, dsb->id),
+				   DSB_NON_POSTED, 0);
+	intel_dsb_noop(dsb, 4);
+}
+
 static void intel_dsb_align_tail(struct intel_dsb *dsb)
 {
 	u32 aligned_tail, tail;

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

@@ -22,6 +22,9 @@ void intel_dsb_reg_write(struct intel_dsb *dsb,
 void intel_dsb_reg_write_masked(struct intel_dsb *dsb,
 				i915_reg_t reg, u32 mask, u32 val);
 void intel_dsb_noop(struct intel_dsb *dsb, int count);
+void intel_dsb_nonpost_start(struct intel_dsb *dsb);
+void intel_dsb_nonpost_end(struct intel_dsb *dsb);
+
 void intel_dsb_commit(struct intel_dsb *dsb,
 		      bool wait_for_vblank);
 void intel_dsb_wait(struct intel_dsb *dsb);