drm/i915/dsb: Extract intel_dsb_{head,tail}()

Extract the code that calculates the DSB_HEAD/TAIL register
values into small helpers. We already have two copies of this,
and soon there will be a third.

Signed-off-by: Ville Syrjälä <[e-mail]>
Signed-off-by: Chaitanya Kumar Borah <[e-mail]>
Reviewed-by: Animesh Manna <[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

···
 	return intel_de_read_fw(display, DSB_CTRL(pipe, dsb_id)) & DSB_STATUS_BUSY;
 }
 
+static unsigned int intel_dsb_head(struct intel_dsb *dsb)
+{
+	return intel_dsb_buffer_ggtt_offset(&dsb->dsb_buf);
+}
+
+static unsigned int intel_dsb_tail(struct intel_dsb *dsb)
+{
+	return intel_dsb_buffer_ggtt_offset(&dsb->dsb_buf) + dsb->free_pos * 4;
+}
+
 static void intel_dsb_ins_align(struct intel_dsb *dsb)
 {
 	/*
···
 	struct intel_display *display = to_intel_display(state->base.dev);
 	struct intel_crtc *crtc = dsb->crtc;
 	enum pipe pipe = crtc->pipe;
-	u32 tail;
 
 	if (drm_WARN_ON(display->drm, dsb->id == chained_dsb->id))
 		return;
 
 	if (!assert_dsb_tail_is_aligned(chained_dsb))
 		return;
-
-	tail = chained_dsb->free_pos * 4;
 
 	intel_dsb_reg_write(dsb, DSB_CTRL(pipe, chained_dsb->id),
 			    ctrl | DSB_ENABLE);
···
 	}
 
 	intel_dsb_reg_write(dsb, DSB_HEAD(pipe, chained_dsb->id),
-			    intel_dsb_buffer_ggtt_offset(&chained_dsb->dsb_buf));
+			    intel_dsb_head(chained_dsb));
 
 	intel_dsb_reg_write(dsb, DSB_TAIL(pipe, chained_dsb->id),
-			    intel_dsb_buffer_ggtt_offset(&chained_dsb->dsb_buf) + tail);
+			    intel_dsb_tail(chained_dsb));
 
 	if (ctrl & DSB_WAIT_FOR_VBLANK) {
 		/*
···
 	struct intel_crtc *crtc = dsb->crtc;
 	struct intel_display *display = to_intel_display(crtc->base.dev);
 	enum pipe pipe = crtc->pipe;
-	u32 tail;
 
 	if (!assert_dsb_tail_is_aligned(dsb))
 		return;
-
-	tail = dsb->free_pos * 4;
 
 	if (is_dsb_busy(display, pipe, dsb->id)) {
 		drm_err(display->drm, "[CRTC:%d:%s] DSB %d is busy\n",
···
 			  dsb_error_int_en(display) | DSB_PROG_INT_EN);
 
 	intel_de_write_fw(display, DSB_HEAD(pipe, dsb->id),
-			  intel_dsb_buffer_ggtt_offset(&dsb->dsb_buf));
+			  intel_dsb_head(dsb));
 
 	if (hw_dewake_scanline >= 0) {
 		int diff, position;
···
 	}
 
 	intel_de_write_fw(display, DSB_TAIL(pipe, dsb->id),
-			  intel_dsb_buffer_ggtt_offset(&dsb->dsb_buf) + tail);
+			  intel_dsb_tail(dsb));
 }
 
 /**