[PATCH v3 2/5] media: atmel-isc: Add prepare and unprepare ops

[Wenyou Yang]

A software write operation to the ISC_CLKEN or ISC_CLKDIS register
requires double clock domain synchronization and is not permitted
when the ISC_SR.SIP is asserted. So add the .prepare and .unprepare
ops to make sure the ISC_CLKSR.SIP is unasserted before the write
operation to the ISC_CLKEN or ISC_CLKDIS register.

Signed-off-by: Wenyou Yang <wenyou.y...@microchip.com>
---

Changes in v3: None
Changes in v2: None

 drivers/media/platform/atmel/atmel-isc-regs.h |  1 +
 drivers/media/platform/atmel/atmel-isc.c      | 30 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/media/platform/atmel/atmel-isc-regs.h 
b/drivers/media/platform/atmel/atmel-isc-regs.h
index 6936ac467609..93e58fcf1d5f 100644
--- a/drivers/media/platform/atmel/atmel-isc-regs.h
+++ b/drivers/media/platform/atmel/atmel-isc-regs.h
@@ -42,6 +42,7 @@
 
 /* ISC Clock Status Register */
 #define ISC_CLKSR               0x00000020
+#define ISC_CLKSR_SIP          BIT(31)
 
 #define ISC_CLK(n)             BIT(n)
 
diff --git a/drivers/media/platform/atmel/atmel-isc.c 
b/drivers/media/platform/atmel/atmel-isc.c
index 991f962b7023..0b15dc1a3a0b 100644
--- a/drivers/media/platform/atmel/atmel-isc.c
+++ b/drivers/media/platform/atmel/atmel-isc.c
@@ -308,6 +308,34 @@ module_param(sensor_preferred, uint, 0644);
 MODULE_PARM_DESC(sensor_preferred,
                 "Sensor is preferred to output the specified format (1-on 
0-off), default 1");
 
+static int isc_wait_clk_stable(struct clk_hw *hw)
+{
+       struct isc_clk *isc_clk = to_isc_clk(hw);
+       struct regmap *regmap = isc_clk->regmap;
+       unsigned long timeout = jiffies + usecs_to_jiffies(1000);
+       unsigned int status;
+
+       while (time_before(jiffies, timeout)) {
+               regmap_read(regmap, ISC_CLKSR, &status);
+               if (!(status & ISC_CLKSR_SIP))
+                       return 0;
+
+               usleep_range(10, 250);
+       }
+
+       return -ETIMEDOUT;
+}
+
+static int isc_clk_prepare(struct clk_hw *hw)
+{
+       return isc_wait_clk_stable(hw);
+}
+
+static void isc_clk_unprepare(struct clk_hw *hw)
+{
+       isc_wait_clk_stable(hw);
+}
+
 static int isc_clk_enable(struct clk_hw *hw)
 {
        struct isc_clk *isc_clk = to_isc_clk(hw);
@@ -459,6 +487,8 @@ static int isc_clk_set_rate(struct clk_hw *hw,
 }
 
 static const struct clk_ops isc_clk_ops = {
+       .prepare        = isc_clk_prepare,
+       .unprepare      = isc_clk_unprepare,
        .enable         = isc_clk_enable,
        .disable        = isc_clk_disable,
        .is_enabled     = isc_clk_is_enabled,
-- 
2.13.0