drm/i915/dsb: Provide intel_dsb_head() and intel_dsb_size()

The upcoming flip queue implementation will need to know the
DSB buffer head and size. Expose those outside intel_dsb.c.

Reviewed-by: Uma Shankar <[e-mail]>
Signed-off-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[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)
+unsigned int intel_dsb_size(struct intel_dsb *dsb)
+{
+	return dsb->free_pos * 4;
+}
+
+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;
+	return intel_dsb_buffer_ggtt_offset(&dsb->dsb_buf) + intel_dsb_size(dsb);
 }
 
 static void intel_dsb_ins_align(struct intel_dsb *dsb)

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

···
 	I915_MAX_DSBS,
 };
 
+unsigned int intel_dsb_size(struct intel_dsb *dsb);
+unsigned int intel_dsb_head(struct intel_dsb *dsb);
 struct intel_dsb *intel_dsb_prepare(struct intel_atomic_state *state,
 				    struct intel_crtc *crtc,
 				    enum intel_dsb_id dsb_id,