[PATCH v3] ARM: Samsung SoC: clksrc-clk: wait for the stable SRC/DIV status.

[MyungJoo Ham]

Many MUX and clock dividers have a status bit so that users can wait
until the status is stable. When corresponding registers are accessed
while a clock is not stable, we may suffer from unexpected errors.

Therefore, we introduce a mechanism to let the operations related with
updating SRC/DIV registers of clksrc-clk wait for the stabilization:
clk_set_parent, clk_set_rate.

In order to use this feature, the definition of clksrc_clk should
include reg_src_stable or reg_div_stable. With effective rec_src_stable
values, clk_set_parent returns with a stabilized SRC register and
with effective rec_div_stable values, clk_set_rate returns with a
stabilized DIV register. If .reg field is null, its (either SRC or DIV)
register's status is not checked and returned without waiting; i.e.,
some MUX/DIV may not need this feature.

When setting reg_*_stable, .size is used to tell the value of "stable".
If .size = 0, the stable status is 0 and if .size = 1, the stable status
is 1.

Signed-off-by: MyungJoo Ham <myungjoo.ham at samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
--
v2:
	- Wait-for-stable loop is described at an inline function.
v3:
	- Stop using clksrc_reg for stable bits. Use "clkstat_reg" for
	  them.

---
 arch/arm/plat-samsung/clock-clksrc.c              |   14 +++++++++++++
 arch/arm/plat-samsung/include/plat/clock-clksrc.h |   22 +++++++++++++++++++++
 2 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/arch/arm/plat-samsung/clock-clksrc.c b/arch/arm/plat-samsung/clock-clksrc.c
index 46d204a..79ae92e 100644
--- a/arch/arm/plat-samsung/clock-clksrc.c
+++ b/arch/arm/plat-samsung/clock-clksrc.c
@@ -50,6 +50,15 @@ static unsigned long s3c_getrate_clksrc(struct clk *clk)
 	return rate;
 }
 
+static inline void s3c_wait_for_stable(struct clkstat_reg *stat)
+{
+	WARN_ON(stat == NULL);
+	if (stat->reg) {
+		do { } while (((__raw_readl(stat->reg) >> stat->shift) & 1)
+				!= stat->stable);
+	}
+}
+
 static int s3c_setrate_clksrc(struct clk *clk, unsigned long rate)
 {
 	struct clksrc_clk *sclk = to_clksrc(clk);
@@ -68,6 +77,8 @@ static int s3c_setrate_clksrc(struct clk *clk, unsigned long rate)
 	val |= (div - 1) << sclk->reg_div.shift;
 	__raw_writel(val, reg);
 
+	s3c_wait_for_stable(&sclk->reg_div_stable);
+
 	return 0;
 }
 
@@ -93,6 +104,9 @@ static int s3c_setparent_clksrc(struct clk *clk, struct clk *parent)
 		clksrc |= src_nr << sclk->reg_src.shift;
 
 		__raw_writel(clksrc, sclk->reg_src.reg);
+
+		s3c_wait_for_stable(&sclk->reg_src_stable);
+
 		return 0;
 	}
 
diff --git a/arch/arm/plat-samsung/include/plat/clock-clksrc.h b/arch/arm/plat-samsung/include/plat/clock-clksrc.h
index 50a8ca7..f1d54da 100644
--- a/arch/arm/plat-samsung/include/plat/clock-clksrc.h
+++ b/arch/arm/plat-samsung/include/plat/clock-clksrc.h
@@ -40,11 +40,30 @@ struct clksrc_reg {
 };
 
 /**
+ * struct clkstat_reg - register definition for clock stat bits
+ * @reg: pointer to the register in virtual memory.
+ * @shift: the shift in bits to where the bitfield is.
+ * @stable: the bit value of stable status.
+ */
+struct clkstat_reg {
+	void __iomem		*reg;
+	unsigned short		shift;
+	unsigned short		stable;
+};
+
+/**
  * struct clksrc_clk - class of clock for newer style samsung devices.
  * @clk: the standard clock representation
  * @sources: the sources for this clock
  * @reg_src: the register definition for selecting the clock's source
  * @reg_div: the register definition for the clock's output divisor
+ * @reg_src_stable: the register definition to probe if reg_src is
+ *    stabilized after the update of reg_src. It is "stabilized" if
+ *    reg[shift] == size. If reg == NULL, this stable reg is not looked
+ *    up. Thus, in S5PV210, size is usually 0.
+ * @reg_div_stable: the register definition to probe if reg_div is
+ *    stabilized after the update of reg_div. Same mechanism with
+ *    reg_src_stable.
  *
  * This clock implements the features required by the newer SoCs where
  * the standard clock block provides an input mux and a post-mux divisor
@@ -61,6 +80,9 @@ struct clksrc_clk {
 
 	struct clksrc_reg	reg_src;
 	struct clksrc_reg	reg_div;
+
+	struct clkstat_reg	reg_src_stable;
+	struct clkstat_reg	reg_div_stable;
 };
 
 /**
-- 
1.6.3.3