clk: fix CLK_SET_RATE_GATE with clock rate protection

CLK_SET_RATE_GATE should prevent any operation which may result in a rate
change or glitch while the clock is prepared/enabled.

IOW, the following sequence is not allowed anymore with CLK_SET_RATE_GATE:
* clk_get()
* clk_prepare_enable()
* clk_get_rate()
* clk_set_rate()

At the moment this is enforced on the leaf clock of the operation, not
along the tree. This problematic because, if a PLL has the CLK_RATE_GATE,
it won't be enforced if the clk_set_rate() is called on its child clocks.

Using clock rate protection, we can now enforce CLK_SET_RATE_GATE along the
clock tree

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20180619134051.16726-3-jbrunet@baylibre.com

drivers/clk/clk.c

@@ -691,6 +691,9 @@ static void clk_core_unprepare(struct clk_core *core)
 	    "Unpreparing critical %s\n", core->name))
 		return;
 
+	if (core->flags & CLK_SET_RATE_GATE)
+		clk_core_rate_unprotect(core);
+
 	if (--core->prepare_count > 0)
 		return;
 
@@ -765,6 +768,16 @@ static int clk_core_prepare(struct clk_core *core)
 
 	core->prepare_count++;
 
+	/*
+	 * CLK_SET_RATE_GATE is a special case of clock protection
+	 * Instead of a consumer claiming exclusive rate control, it is
+	 * actually the provider which prevents any consumer from making any
+	 * operation which could result in a rate change or rate glitch while
+	 * the clock is prepared.
+	 */
+	if (core->flags & CLK_SET_RATE_GATE)
+		clk_core_rate_protect(core);
+
 	return 0;
 unprepare:
 	clk_core_unprepare(core->parent);
@@ -1888,9 +1901,6 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
 	if (clk_core_rate_is_protected(core))
 		return -EBUSY;
 
-	if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
-		return -EBUSY;
-
 	/* calculate new rates and get the topmost changed clock */
 	top = clk_calc_new_rates(core, req_rate);
 	if (!top)