Am 21.02.2017 um 22:21 schrieb Neil Armstrong:

On 02/21/2017 12:26 PM, Heiner Kallweit wrote:

quoted

Add handling of RNG0 clock to the driver.

Signed-off-by: Heiner Kallweit <redacted>
---
v2:
- consider that clock is optional
- use managed call to clk_disable_unprepare to ensure that
  cleaning up is done in the right order if driver is removed
---
 drivers/char/hw_random/meson-rng.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/char/hw_random/meson-rng.c b/drivers/char/hw_random/meson-rng.c
index 119d6984..2e23be80 100644
--- a/drivers/char/hw_random/meson-rng.c
+++ b/drivers/char/hw_random/meson-rng.c

@@ -62,6 +62,7 @@
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/of.h>
+#include <linux/clk.h>
 
 #define RNG_DATA 0x00
 

@@ -69,6 +70,7 @@ struct meson_rng_data {
 	void __iomem *base;
 	struct platform_device *pdev;
 	struct hwrng rng;
+	struct clk *core_clk;
 };
 
 static int meson_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)

@@ -81,11 +83,17 @@ static int meson_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 	return sizeof(u32);
 }
 
+static void meson_rng_clk_disable(void *clk)
+{
+	clk_disable_unprepare(clk);
+}
+
 static int meson_rng_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct meson_rng_data *data;
 	struct resource *res;
+	int ret;
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)

@@ -98,6 +106,20 @@ static int meson_rng_probe(struct platform_device *pdev)
 	if (IS_ERR(data->base))
 		return PTR_ERR(data->base);
 
+	data->core_clk = devm_clk_get(dev, "core");
+	if (IS_ERR(data->core_clk))
+		data->core_clk = NULL;
+
+	if (data->core_clk) {

This "if" is useless, if core_clk is NULL, this will work also.

Regarding clk_prepare_enable you're right. However we need this "if" for
the call to devm_add_action_or_reset because we can't provide a NULL
pointer as data argument.
And including clk_prepare_enable in the if clause creates no overhead
and is clearer IMHO.

quoted

+		ret = clk_prepare_enable(data->core_clk);
+		if (ret)
+			return ret;
+		ret = devm_add_action_or_reset(dev, meson_rng_clk_disable,
+					       data->core_clk);
+		if (ret)
+			return ret;
+	}
+
 	data->rng.name = pdev->name;
 	data->rng.read = meson_rng_read;
 

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