clk: divider: add CLK_DIVIDER_HIWORD_MASK flag

In both Hisilicon & Rockchip Cortex-A9 based chips, they don't use the
paradigm of reading-changing-writing the register contents.
Instead they use a hiword mask to indicate the changed bits.

When b01 should be set as setting divider, it also needs to indicate
the change by setting hiword mask (b11 << 16).

The patch adds divider flag for this usage.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

drivers/clk/clk-divider.c

@@ -227,8 +227,12 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
 	if (divider->lock)
 		spin_lock_irqsave(divider->lock, flags);
 
-	val = readl(divider->reg);
-	val &= ~(div_mask(divider) << divider->shift);
+	if (divider->flags & CLK_DIVIDER_HIWORD_MASK) {
+		val = div_mask(divider) << (divider->shift + 16);
+	} else {
+		val = readl(divider->reg);
+		val &= ~(div_mask(divider) << divider->shift);
+	}
 	val |= value << divider->shift;
 	writel(val, divider->reg);
 
@@ -255,6 +259,13 @@ static struct clk *_register_divider(struct device *dev, const char *name,
 	struct clk *clk;
 	struct clk_init_data init;
 
+	if (clk_divider_flags & CLK_DIVIDER_HIWORD_MASK) {
+		if (width + shift > 16) {
+			pr_warn("divider value exceeds LOWORD field\n");
+			return ERR_PTR(-EINVAL);
+		}
+	}
+
 	/* allocate the divider */
 	div = kzalloc(sizeof(struct clk_divider), GFP_KERNEL);
 	if (!div) {

include/linux/clk-provider.h

@@ -257,6 +257,10 @@ struct clk_div_table {
  *	Some hardware implementations gracefully handle this case and allow a
  *	zero divisor by not modifying their input clock
  *	(divide by one / bypass).
+ * CLK_DIVIDER_HIWORD_MASK - The divider settings are only in lower 16-bit
+ *   of this register, and mask of divider bits are in higher 16-bit of this
+ *   register.  While setting the divider bits, higher 16-bit should also be
+ *   updated to indicate changing divider bits.
  */
 struct clk_divider {
 	struct clk_hw	hw;
@@ -271,6 +275,7 @@ struct clk_divider {
 #define CLK_DIVIDER_ONE_BASED		BIT(0)
 #define CLK_DIVIDER_POWER_OF_TWO	BIT(1)
 #define CLK_DIVIDER_ALLOW_ZERO		BIT(2)
+#define CLK_DIVIDER_HIWORD_MASK		BIT(3)
 
 extern const struct clk_ops clk_divider_ops;
 struct clk *clk_register_divider(struct device *dev, const char *name,