ARM: shmobile: wait for MSTP clock status to toggle, when enabling it

On r-/sh-mobile SoCs MSTP clocks are used by the runtime PM to dynamically
enable and disable peripheral clocks. To make sure the clock has really
started we have to read back its status register until it confirms success.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

drivers/sh/clk/cpg.c

@@ -36,9 +36,47 @@ static void sh_clk_write(int value, struct clk *clk)
 		iowrite32(value, clk->mapped_reg);
 }
 
+static unsigned int r8(const void __iomem *addr)
+{
+	return ioread8(addr);
+}
+
+static unsigned int r16(const void __iomem *addr)
+{
+	return ioread16(addr);
+}
+
+static unsigned int r32(const void __iomem *addr)
+{
+	return ioread32(addr);
+}
+
 static int sh_clk_mstp_enable(struct clk *clk)
 {
 	sh_clk_write(sh_clk_read(clk) & ~(1 << clk->enable_bit), clk);
+	if (clk->status_reg) {
+		unsigned int (*read)(const void __iomem *addr);
+		int i;
+		void __iomem *mapped_status = (phys_addr_t)clk->status_reg -
+			(phys_addr_t)clk->enable_reg + clk->mapped_reg;
+
+		if (clk->flags & CLK_ENABLE_REG_8BIT)
+			read = r8;
+		else if (clk->flags & CLK_ENABLE_REG_16BIT)
+			read = r16;
+		else
+			read = r32;
+
+		for (i = 1000;
+		     (read(mapped_status) & (1 << clk->enable_bit)) && i;
+		     i--)
+			cpu_relax();
+		if (!i) {
+			pr_err("cpg: failed to enable %p[%d]\n",
+			       clk->enable_reg, clk->enable_bit);
+			return -ETIMEDOUT;
+		}
+	}
 	return 0;
 }