drm: rcar-du: Configure DPAD0 routing through last group on Gen3

On Gen3 SoCs DPAD0 routing is configured through the last CRTC group,
unlike on Gen2 where it is configured through the first CRTC group. Fix
the driver accordingly.

Fixes: 2427b30377 ("drm: rcar-du: Add R8A7795 device support")
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_group.c

@@ -212,6 +212,9 @@ void rcar_du_group_restart(struct rcar_du_group *rgrp)
 
 int rcar_du_set_dpad0_vsp1_routing(struct rcar_du_device *rcdu)
 {
+	struct rcar_du_group *rgrp;
+	struct rcar_du_crtc *crtc;
+	unsigned int index;
 	int ret;
 
 	if (!rcar_du_has(rcdu, RCAR_DU_FEATURE_EXT_CTRL_REGS))
@@ -219,17 +222,22 @@ int rcar_du_set_dpad0_vsp1_routing(struct rcar_du_device *rcdu)
 
 	/*
 	 * RGB output routing to DPAD0 and VSP1D routing to DU0/1/2 are
-	 * configured in the DEFR8 register of the first group. As this function
-	 * can be called with the DU0 and DU1 CRTCs disabled, we need to enable
-	 * the first group clock before accessing the register.
+	 * configured in the DEFR8 register of the first group on Gen2 and the
+	 * last group on Gen3. As this function can be called with the DU
+	 * channels of the corresponding CRTCs disabled, we need to enable the
+	 * group clock before accessing the register.
 	 */
-	ret = clk_prepare_enable(rcdu->crtcs[0].clock);
+	index = rcdu->info->gen < 3 ? 0 : DIV_ROUND_UP(rcdu->num_crtcs, 2) - 1;
+	rgrp = &rcdu->groups[index];
+	crtc = &rcdu->crtcs[index * 2];
+
+	ret = clk_prepare_enable(crtc->clock);
 	if (ret < 0)
 		return ret;
 
-	rcar_du_group_setup_defr8(&rcdu->groups[0]);
+	rcar_du_group_setup_defr8(rgrp);
 
-	clk_disable_unprepare(rcdu->crtcs[0].clock);
+	clk_disable_unprepare(crtc->clock);
 
 	return 0;
 }