clk: meson: meson8b: mark fclk_div2 gate clocks as CLK_IS_CRITICAL

Until commit 05f814402d6174 ("clk: meson: add fdiv clock gates") we
relied on the bootloader to enable the fclk_div clock gates. It turns
out that our clock tree is incomplete at least on Meson8b (tested with
an Odroid-C1, which uses an RGMII PHY) because after the mentioned
commit Ethernet is not working anymore (no RX/TX activity can be seen).
At the same time Ethernet was still working on Meson8m2 with a RMII PHY.

Testing has shown that as soon as "fclk_div2" is disabled Ethernet stops
working on Odroid-C1. Unfortunately it's currently not clear what the
Ethernet controller IP block uses the fclk_div2 clock for. Mark the
clock as CLK_IS_CRITICAL to keep it enabled (as it's already enabled by
most bootloaders by default, which is why we didn't notice it before).

Fixes: 05f814402d6174 ("clk: meson: add fdiv clock gates")
Cc: stable@vger.kernel.org
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>

drivers/clk/meson/meson8b.c

@@ -232,6 +232,13 @@ static struct clk_regmap meson8b_fclk_div2 = {
 		.ops = &clk_regmap_gate_ops,
 		.parent_names = (const char *[]){ "fclk_div2_div" },
 		.num_parents = 1,
+		/*
+		 * FIXME: Ethernet with a RGMII PHYs is not working if
+		 * fclk_div2 is disabled. it is currently unclear why this
+		 * is. keep it enabled until the Ethernet driver knows how
+		 * to manage this clock.
+		 */
+		.flags = CLK_IS_CRITICAL,
 	},
 };