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[PATCH v2 2/5] media: atmel-isc: Add prepare and unprepare ops

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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.yang@microchip.com>
---

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 78114193af4c..8b9c1cafa348 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

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[PATCH v2 2/5] media: atmel-isc: Add prepare and unprepare ops Wenyou Yang <wenyou.yang@microchip.com> - 2017-09-18 08:50 +0200

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