media: v4l2-common: Add a helper for obtaining the clock producer

Introduce a helper for v4l2 sensor drivers on both DT- and ACPI-based
platforms to retrieve a reference to the clock producer from firmware.

This helper behaves the same as devm_clk_get() except where there is
no clock producer like in ACPI-based platforms.

For ACPI-based platforms the function will read the "clock-frequency"
ACPI _DSD property and register a fixed frequency clock with the frequency
indicated in the property.

This function also handles the special ACPI-based system case where:
. The clock-frequency _DSD property is present.
. A reference to the clock producer is present, where the clock is provided
  by a camera sensor PMIC driver (e.g. int3472/tps68470.c)
In this case try to set the clock-frequency value to the provided clock.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

drivers/media/v4l2-core/v4l2-common.c

@@ -34,6 +34,9 @@
  * Added Gerd Knorrs v4l1 enhancements (Justin Schoeman)
  */
 
+#include <linux/clk.h>
+#include <linux/clkdev.h>
+#include <linux/clk-provider.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
@@ -705,3 +708,52 @@ int v4l2_link_freq_to_bitmap(struct device *dev, const u64 *fw_link_freqs,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(v4l2_link_freq_to_bitmap);
+
+struct clk *devm_v4l2_sensor_clk_get(struct device *dev, const char *id)
+{
+	const char *clk_id __free(kfree) = NULL;
+	struct clk_hw *clk_hw;
+	struct clk *clk;
+	bool of_node;
+	u32 rate;
+	int ret;
+
+	clk = devm_clk_get_optional(dev, id);
+	if (IS_ERR(clk))
+		return clk;
+
+	ret = device_property_read_u32(dev, "clock-frequency", &rate);
+	of_node = is_of_node(dev_fwnode(dev));
+
+	if (clk) {
+		if (!ret && !of_node) {
+			ret = clk_set_rate(clk, rate);
+			if (ret) {
+				dev_err(dev, "Failed to set clock rate: %u\n",
+					rate);
+				return ERR_PTR(ret);
+			}
+		}
+		return clk;
+	}
+
+	if (!IS_ENABLED(CONFIG_COMMON_CLK) || of_node)
+		return ERR_PTR(-ENOENT);
+
+	if (ret)
+		return ERR_PTR(ret == -EINVAL ? -EPROBE_DEFER : ret);
+
+	if (!id) {
+		clk_id = kasprintf(GFP_KERNEL, "clk-%s", dev_name(dev));
+		if (!clk_id)
+			return ERR_PTR(-ENOMEM);
+		id = clk_id;
+	}
+
+	clk_hw = devm_clk_hw_register_fixed_rate(dev, id, NULL, 0, rate);
+	if (IS_ERR(clk_hw))
+		return ERR_CAST(clk_hw);
+
+	return clk_hw->clk;
+}
+EXPORT_SYMBOL_GPL(devm_v4l2_sensor_clk_get);

include/media/v4l2-common.h

@@ -97,6 +97,7 @@ int v4l2_ctrl_query_fill(struct v4l2_queryctrl *qctrl,
 
 /* ------------------------------------------------------------------------- */
 
+struct clk;
 struct v4l2_device;
 struct v4l2_subdev;
 struct v4l2_subdev_ops;
@@ -620,6 +621,32 @@ int v4l2_link_freq_to_bitmap(struct device *dev, const u64 *fw_link_freqs,
 			     unsigned int num_of_driver_link_freqs,
 			     unsigned long *bitmap);
 
+/**
+ * devm_v4l2_sensor_clk_get - lookup and obtain a reference to a clock producer
+ *	for a camera sensor.
+ *
+ * @dev: device for v4l2 sensor clock "consumer"
+ * @id: clock consumer ID
+ *
+ * This function behaves the same way as devm_clk_get() except where there
+ * is no clock producer like in ACPI-based platforms.
+ *
+ * For ACPI-based platforms, the function will read the "clock-frequency"
+ * ACPI _DSD property and register a fixed-clock with the frequency indicated
+ * in the property.
+ *
+ * This function also handles the special ACPI-based system case where:
+ *
+ * * The clock-frequency _DSD property is present.
+ * * A reference to the clock producer is present, where the clock is provided
+ *   by a camera sensor PMIC driver (e.g. int3472/tps68470.c)
+ *
+ * In this case try to set the clock-frequency value to the provided clock.
+ *
+ * Returns a pointer to a struct clk on success or an error pointer on failure.
+ */
+struct clk *devm_v4l2_sensor_clk_get(struct device *dev, const char *id);
+
 static inline u64 v4l2_buffer_get_timestamp(const struct v4l2_buffer *buf)
 {
 	/*