ARM: imx: add shared gate clock support

It's quite common on i.MX that one gate bit controls the gating of
multiple clocks, i.e. this is a shared gate.  The patch adds the
function imx_clk_gate2_shared() for such case.  The clocks controlled
by the same gate bits should call this function with a pointer to a
single share count variable, so that the gate bits will only be
operated on the first enabling and the last disabling of these shared
gate clocks.

Thanks to Gerhard Sittig <gsi@denx.de> for this idea.
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

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

@@ -33,6 +33,7 @@ struct clk_gate2 {
 	u8		bit_idx;
 	u8		flags;
 	spinlock_t	*lock;
+	unsigned int	*share_count;
 };
 
 #define to_clk_gate2(_hw) container_of(_hw, struct clk_gate2, hw)
@@ -45,10 +46,14 @@ static int clk_gate2_enable(struct clk_hw *hw)
 
 	spin_lock_irqsave(gate->lock, flags);
 
+	if (gate->share_count && (*gate->share_count)++ > 0)
+		goto out;
+
 	reg = readl(gate->reg);
 	reg |= 3 << gate->bit_idx;
 	writel(reg, gate->reg);
 
+out:
 	spin_unlock_irqrestore(gate->lock, flags);
 
 	return 0;
@@ -62,10 +67,14 @@ static void clk_gate2_disable(struct clk_hw *hw)
 
 	spin_lock_irqsave(gate->lock, flags);
 
+	if (gate->share_count && --(*gate->share_count) > 0)
+		goto out;
+
 	reg = readl(gate->reg);
 	reg &= ~(3 << gate->bit_idx);
 	writel(reg, gate->reg);
 
+out:
 	spin_unlock_irqrestore(gate->lock, flags);
 }
 
@@ -91,7 +100,8 @@ static struct clk_ops clk_gate2_ops = {
 struct clk *clk_register_gate2(struct device *dev, const char *name,
 		const char *parent_name, unsigned long flags,
 		void __iomem *reg, u8 bit_idx,
-		u8 clk_gate2_flags, spinlock_t *lock)
+		u8 clk_gate2_flags, spinlock_t *lock,
+		unsigned int *share_count)
 {
 	struct clk_gate2 *gate;
 	struct clk *clk;
@@ -106,6 +116,7 @@ struct clk *clk_register_gate2(struct device *dev, const char *name,
 	gate->bit_idx = bit_idx;
 	gate->flags = clk_gate2_flags;
 	gate->lock = lock;
+	gate->share_count = share_count;
 
 	init.name = name;
 	init.ops = &clk_gate2_ops;

arch/arm/mach-imx/clk.h

@@ -28,7 +28,8 @@ struct clk *imx_clk_pllv3(enum imx_pllv3_type type, const char *name,
 struct clk *clk_register_gate2(struct device *dev, const char *name,
 		const char *parent_name, unsigned long flags,
 		void __iomem *reg, u8 bit_idx,
-		u8 clk_gate_flags, spinlock_t *lock);
+		u8 clk_gate_flags, spinlock_t *lock,
+		unsigned int *share_count);
 
 struct clk * imx_obtain_fixed_clock(
 			const char *name, unsigned long rate);
@@ -37,7 +38,15 @@ static inline struct clk *imx_clk_gate2(const char *name, const char *parent,
 		void __iomem *reg, u8 shift)
 {
 	return clk_register_gate2(NULL, name, parent, CLK_SET_RATE_PARENT, reg,
-			shift, 0, &imx_ccm_lock);
+			shift, 0, &imx_ccm_lock, NULL);
+}
+
+static inline struct clk *imx_clk_gate2_shared(const char *name,
+		const char *parent, void __iomem *reg, u8 shift,
+		unsigned int *share_count)
+{
+	return clk_register_gate2(NULL, name, parent, CLK_SET_RATE_PARENT, reg,
+			shift, 0, &imx_ccm_lock, share_count);
 }
 
 struct clk *imx_clk_pfd(const char *name, const char *parent_name,