iio: adc: ad7124: add clock output support

Add support for the AD7124's internal clock output. If the #clock-cells
property is present, turn on the internal clock output during probe.

If both the clocks and #clock-names properties are present (not allowed
by devicetree bindings), assume that an external clock is being used so
that we don't accidentally have two outputs fighting each other.

Signed-off-by: David Lechner <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/ad7124.c

···
  */
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/clk.h>
+#include <linux/clk-provider.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/err.h>
···
 #include <linux/property.h>
 #include <linux/regulator/consumer.h>
 #include <linux/spi/spi.h>
+#include <linux/sprintf.h>
 #include <linux/units.h>
 
 #include <linux/iio/iio.h>
···
 		}
 
 		clk_sel = AD7124_ADC_CONTROL_CLK_SEL_INT;
+		st->clk_hz = AD7124_INT_CLK_HZ;
+	} else if (!device_property_present(dev, "clocks") &&
+		   device_property_present(dev, "#clock-cells")) {
+#ifdef CONFIG_COMMON_CLK
+		struct clk_hw *clk_hw;
+
+		const char *name __free(kfree) = kasprintf(GFP_KERNEL, "%pfwP-clk",
+							   dev_fwnode(dev));
+		if (!name)
+			return -ENOMEM;
+
+		clk_hw = devm_clk_hw_register_fixed_rate(dev, name, NULL, 0,
+							 AD7124_INT_CLK_HZ);
+		if (IS_ERR(clk_hw))
+			return dev_err_probe(dev, PTR_ERR(clk_hw),
+					     "Failed to register clock provider\n");
+
+		ret = devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get,
+						  clk_hw);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "Failed to add clock provider\n");
+#endif
+
+		/*
+		 * Treat the clock as always on. This way we don't have to deal
+		 * with someone trying to enable/disable the clock while we are
+		 * reading samples.
+		 */
+		clk_sel = AD7124_ADC_CONTROL_CLK_SEL_INT_OUT;
 		st->clk_hz = AD7124_INT_CLK_HZ;
 	} else {
 		struct clk *clk;