ARM: imx: fix shared gate clock

Let's say clock A and B are two gate clocks that share the same register
bit in hardware.  Therefore they are registered as shared gate clocks
with imx_clk_gate2_shared().

In a scenario that only clock A is enabled by clk_enable(A) while B is
not used, the shared gate will be unexpectedly disabled in hardware.
It happens because clk_enable(A) increments the share_count from 0 to 1,
while clock B is unused to clock core, and therefore the core function
will just disable B by calling clk->ops->disable() directly.  The
consequence of that call is share_count is decremented to 0 and the gate
is disabled in hardware, even though clock A is still in use.

The patch fixes the issue by initializing the share_count per hardware
state and returns enable state per share_count from .is_enabled() hook,
in case it's a shared gate.

While at it, add a check in clk_gate2_disable() to ensure it's never
called with a zero share_count.
Reported-by: Fabio Estevam <fabio.estevam@freescale.com>
Fixes: f9f28cdf ("ARM: imx: add shared gate clock support")
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/mach-imx/clk-gate2.c

@@ -67,8 +67,12 @@ static void clk_gate2_disable(struct clk_hw *hw)
 
 	spin_lock_irqsave(gate->lock, flags);
 
-	if (gate->share_count && --(*gate->share_count) > 0)
+	if (gate->share_count) {
+		if (WARN_ON(*gate->share_count == 0))
 			goto out;
+		else if (--(*gate->share_count) > 0)
+			goto out;
+	}
 
 	reg = readl(gate->reg);
 	reg &= ~(3 << gate->bit_idx);
@@ -78,19 +82,26 @@ static void clk_gate2_disable(struct clk_hw *hw)
 	spin_unlock_irqrestore(gate->lock, flags);
 }
 
-static int clk_gate2_is_enabled(struct clk_hw *hw)
+static int clk_gate2_reg_is_enabled(void __iomem *reg, u8 bit_idx)
 {
-	u32 reg;
-	struct clk_gate2 *gate = to_clk_gate2(hw);
+	u32 val = readl(reg);
 
-	reg = readl(gate->reg);
-
-	if (((reg >> gate->bit_idx) & 1) == 1)
+	if (((val >> bit_idx) & 1) == 1)
 		return 1;
 
 	return 0;
 }
 
+static int clk_gate2_is_enabled(struct clk_hw *hw)
+{
+	struct clk_gate2 *gate = to_clk_gate2(hw);
+
+	if (gate->share_count)
+		return !!(*gate->share_count);
+	else
+		return clk_gate2_reg_is_enabled(gate->reg, gate->bit_idx);
+}
+
 static struct clk_ops clk_gate2_ops = {
 	.enable = clk_gate2_enable,
 	.disable = clk_gate2_disable,
@@ -116,6 +127,10 @@ struct clk *clk_register_gate2(struct device *dev, const char *name,
 	gate->bit_idx = bit_idx;
 	gate->flags = clk_gate2_flags;
 	gate->lock = lock;
+
+	/* Initialize share_count per hardware state */
+	if (share_count)
+		*share_count = clk_gate2_reg_is_enabled(reg, bit_idx) ? 1 : 0;
 	gate->share_count = share_count;
 
 	init.name = name;