[PATCH v4 2/2] i2c: designware: Add support for a peripheral clock

[Gareth Williams <gareth.williams.jx@xxxxxxxxxxx>]

From: Phil Edworthy <phil.edworthy@xxxxxxxxxxx>

The Synopsys I2C Controller has a peripheral clock, but most SoCs hide
this away. However, some SoCs need explicit enabling of the peripheral
clock in order to access the registers. Therefore, add support for an
optional peripheral clock.

Signed-off-by: Phil Edworthy <phil.edworthy@xxxxxxxxxxx>
Signed-off-by: Gareth Williams <gareth.williams.jx@xxxxxxxxxxx>
Acked-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
v4:
 - Updated comments to reference "peripheral clock" 
   instead of "bus clock".
 - Added Wolfram's Acked-by
v3:
 - busclk renamed to pclk.
 - Added comment with dw_i2c_dev struct definition describing pclk.
 - Added enable rollback of first clock if second fails to enable.
v2:
 - Use new devm_clk_get_optional() function as it simplifies handling when
   the optional clock is not present.
---
 drivers/i2c/busses/i2c-designware-common.c  | 18 ++++++++++++++++--
 drivers/i2c/busses/i2c-designware-core.h    |  2 ++
 drivers/i2c/busses/i2c-designware-platdrv.c |  5 +++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
index a473011..e807aa2 100644
--- a/drivers/i2c/busses/i2c-designware-common.c
+++ b/drivers/i2c/busses/i2c-designware-common.c
@@ -251,13 +251,27 @@ unsigned long i2c_dw_clk_rate(struct dw_i2c_dev *dev)
 
 int i2c_dw_prepare_clk(struct dw_i2c_dev *dev, bool prepare)
 {
+	int ret;
+
 	if (IS_ERR(dev->clk))
 		return PTR_ERR(dev->clk);
 
-	if (prepare)
-		return clk_prepare_enable(dev->clk);
+	if (prepare) {
+		/* Optional peripheral clock */
+		ret = clk_prepare_enable(dev->pclk);
+		if (ret)
+			return ret;
+
+		ret = clk_prepare_enable(dev->clk);
+		if (ret)
+			clk_disable_unprepare(dev->pclk);
+
+		return ret;
+	}
 
 	clk_disable_unprepare(dev->clk);
+	clk_disable_unprepare(dev->pclk);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(i2c_dw_prepare_clk);
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index b4a0b2b..e88c711 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -177,6 +177,7 @@
  * @base: IO registers pointer
  * @cmd_complete: tx completion indicator
  * @clk: input reference clock
+ * @pclk: clock required to access the registers
  * @slave: represent an I2C slave device
  * @cmd_err: run time hadware error code
  * @msgs: points to an array of messages currently being transferred
@@ -226,6 +227,7 @@ struct dw_i2c_dev {
 	void __iomem		*ext;
 	struct completion	cmd_complete;
 	struct clk		*clk;
+	struct clk		*pclk;
 	struct reset_control	*rst;
 	struct i2c_client		*slave;
 	u32			(*get_clk_rate_khz) (struct dw_i2c_dev *dev);
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index 9eaac3b..03fff6a 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -346,6 +346,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
 	else
 		i2c_dw_configure_master(dev);
 
+	/* Optional peripheral clock */
+	dev->pclk = devm_clk_get_optional(&pdev->dev, "pclk");
+	if (IS_ERR(dev->pclk))
+		return PTR_ERR(dev->pclk);
+
 	dev->clk = devm_clk_get(&pdev->dev, NULL);
 	if (!i2c_dw_prepare_clk(dev, true)) {
 		u64 clk_khz;
-- 
2.7.4