clocksource: armada-370-xp: Use the reference clock on A375 SoC

The 25 MHz reference clock has better stability so its use is preferred over the
core clock.

This commit takes advantage of the already introduced Armada 375 devicetree
compatible string and adds a new timer initialization. If available, the timer
will use the reference clock (named as 'fixed'). Otherwise, it falls back to the
previous behavior.

Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Wim Van Sebroeck <wim@iguana.be>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/marvell,armada-370-xp-timer.txt

@@ -2,8 +2,10 @@ Marvell Armada 370 and Armada XP Timers
 ---------------------------------------
 
 Required properties:
-- compatible: Should be either "marvell,armada-370-timer" or
-  "marvell,armada-xp-timer" as appropriate.
+- compatible: Should be one of the following
+              "marvell,armada-370-timer",
+	      "marvell,armada-375-timer",
+	      "marvell,armada-xp-timer".
 - interrupts: Should contain the list of Global Timer interrupts and
   then local timer interrupts
 - reg: Should contain location and length for timers register. First
@@ -13,7 +15,8 @@ Required properties:
 Clocks required for compatible = "marvell,armada-370-timer":
 - clocks : Must contain a single entry describing the clock input
 
-Clocks required for compatible = "marvell,armada-xp-timer":
+Clocks required for compatibles = "marvell,armada-xp-timer",
+				  "marvell,armada-375-timer":
 - clocks : Must contain an entry for each entry in clock-names.
 - clock-names : Must include the following entries:
   "nbclk" (L2/coherency fabric clock),

drivers/clocksource/time-armada-370-xp.c

@@ -301,6 +301,34 @@ static void __init armada_xp_timer_init(struct device_node *np)
 CLOCKSOURCE_OF_DECLARE(armada_xp, "marvell,armada-xp-timer",
 		       armada_xp_timer_init);
 
+static void __init armada_375_timer_init(struct device_node *np)
+{
+	struct clk *clk;
+
+	clk = of_clk_get_by_name(np, "fixed");
+	if (!IS_ERR(clk)) {
+		clk_prepare_enable(clk);
+		timer_clk = clk_get_rate(clk);
+	} else {
+
+		/*
+		 * This fallback is required in order to retain proper
+		 * devicetree backwards compatibility.
+		 */
+		clk = of_clk_get(np, 0);
+
+		/* Must have at least a clock */
+		BUG_ON(IS_ERR(clk));
+		clk_prepare_enable(clk);
+		timer_clk = clk_get_rate(clk) / TIMER_DIVIDER;
+		timer25Mhz = false;
+	}
+
+	armada_370_xp_timer_common_init(np);
+}
+CLOCKSOURCE_OF_DECLARE(armada_375, "marvell,armada-375-timer",
+		       armada_375_timer_init);
+
 static void __init armada_370_timer_init(struct device_node *np)
 {
 	struct clk *clk = of_clk_get(np, 0);