clk: rockchip: add a dummy clock for the watchdog pclk on rk3399

Like rk3288, the pclk supplying the watchdog is controlled via the
SGRF register area. Additionally the SGRF isn't even writable in
every boot mode.

But still the clock control is available and in the future someone
might want to use it. Therefore define a simple clock for the time
being so that the watchdog driver can read its rate.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Reviewed-by: Stephen Barber <smbarber@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

drivers/clk/rockchip/clk-rk3399.c

@@ -1498,6 +1498,7 @@ static void __init rk3399_clk_init(struct device_node *np)
 {
 	struct rockchip_clk_provider *ctx;
 	void __iomem *reg_base;
+	struct clk *clk;
 
 	reg_base = of_iomap(np, 0);
 	if (!reg_base) {
@@ -1511,6 +1512,14 @@ static void __init rk3399_clk_init(struct device_node *np)
 		return;
 	}
 
+	/* Watchdog pclk is controlled by RK3399 SECURE_GRF_SOC_CON3[8]. */
+	clk = clk_register_fixed_factor(NULL, "pclk_wdt", "pclk_alive", 0, 1, 1);
+	if (IS_ERR(clk))
+		pr_warn("%s: could not register clock pclk_wdt: %ld\n",
+			__func__, PTR_ERR(clk));
+	else
+		rockchip_clk_add_lookup(ctx, clk, PCLK_WDT);
+
 	rockchip_clk_register_plls(ctx, rk3399_pll_clks,
 				   ARRAY_SIZE(rk3399_pll_clks), -1);