drm/i915/dsb: add intel_dsb_gosub_finish()

A DSB buffer which will be used for GOSUB execution does not need
the DEWAKE mechanism but still need to be 64 bit aligned. Add helper
to finish preparation of a dsb buffer to be executed with GOSUB
instruction.

v2: Add a cacheline of noops at the end of GOSUB buffer (Ville)

Signed-off-by: Chaitanya Kumar Borah <[e-mail]>
Reviewed-by: Uma Shankar <[e-mail]>
Signed-off-by: Animesh Manna <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

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

···
 	intel_dsb_align_tail(dsb);
 }
 
+void intel_dsb_gosub_finish(struct intel_dsb *dsb)
+{
+	intel_dsb_align_tail(dsb);
+
+	/*
+	 * "All subroutines called by the GOSUB instruction
+	 *  must end with a cacheline of NOPs"
+	 */
+	intel_dsb_noop(dsb, 8);
+
+	intel_dsb_buffer_flush_map(&dsb->dsb_buf);
+}
+
 void intel_dsb_finish(struct intel_dsb *dsb)
 {
 	struct intel_crtc *crtc = dsb->crtc;

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

···
 				    enum intel_dsb_id dsb_id,
 				    unsigned int max_cmds);
 void intel_dsb_finish(struct intel_dsb *dsb);
+void intel_dsb_gosub_finish(struct intel_dsb *dsb);
 void intel_dsb_cleanup(struct intel_dsb *dsb);
 void intel_dsb_reg_write(struct intel_dsb *dsb,
 			 i915_reg_t reg, u32 val);