mfd: simple-mfd-i2c: Add support for registering devices via MFD cells

More devices are cropping up requiring only Regmap initialisation and
child registration functionality.  We currently only support that if
all required devices are represented by their own Device Tree nodes
complete with compatible strings.

However, not everyone is happy with adding empty nodes that provide no
additional device information into the Device Tree.

Rather than have a plethora of mostly empty, function-less drivers in
MFD, we'll support those simple cases in here instead via MFD cells.

Cc: Mark Brown <broonie@kernel.org>
Tested-by: Michael Walle <michael@walle.cc>
Reviewed-by: Alistair Francis <alistair@alistair23.me>
Tested-by: Alistair Francis <alistair@alistair23.me>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/simple-mfd-i2c.c

@@ -2,39 +2,64 @@
 /*
  * Simple MFD - I2C
  *
+ * Author(s):
+ * 	Michael Walle <michael@walle.cc>
+ * 	Lee Jones <lee.jones@linaro.org>
+ *
  * This driver creates a single register map with the intention for it to be
  * shared by all sub-devices.  Children can use their parent's device structure
  * (dev.parent) in order to reference it.
  *
  * Once the register map has been successfully initialised, any sub-devices
- * represented by child nodes in Device Tree will be subsequently registered.
+ * represented by child nodes in Device Tree or via the MFD cells in this file
+ * will be subsequently registered.
  */
 
 #include <linux/i2c.h>
 #include <linux/kernel.h>
+#include <linux/mfd/core.h>
 #include <linux/module.h>
 #include <linux/of_platform.h>
 #include <linux/regmap.h>
 
-static const struct regmap_config simple_regmap_config = {
+#include "simple-mfd-i2c.h"
+
+static const struct regmap_config regmap_config_8r_8v = {
 	.reg_bits = 8,
 	.val_bits = 8,
 };
 
 static int simple_mfd_i2c_probe(struct i2c_client *i2c)
 {
-	const struct regmap_config *config;
+	const struct simple_mfd_data *simple_mfd_data;
+	const struct regmap_config *regmap_config;
 	struct regmap *regmap;
+	int ret;
 
-	config = device_get_match_data(&i2c->dev);
-	if (!config)
-		config = &simple_regmap_config;
+	simple_mfd_data = device_get_match_data(&i2c->dev);
 
-	regmap = devm_regmap_init_i2c(i2c, config);
+	/* If no regmap_config is specified, use the default 8reg and 8val bits */
+	if (!simple_mfd_data || !simple_mfd_data->regmap_config)
+		regmap_config = &regmap_config_8r_8v;
+	else
+		regmap_config = simple_mfd_data->regmap_config;
+
+	regmap = devm_regmap_init_i2c(i2c, regmap_config);
 	if (IS_ERR(regmap))
 		return PTR_ERR(regmap);
 
-	return devm_of_platform_populate(&i2c->dev);
+	/* If no MFD cells are spedified, use register the DT child nodes instead */
+	if (!simple_mfd_data || !simple_mfd_data->mfd_cell)
+		return devm_of_platform_populate(&i2c->dev);
+
+	ret = devm_mfd_add_devices(&i2c->dev, PLATFORM_DEVID_AUTO,
+				   simple_mfd_data->mfd_cell,
+				   simple_mfd_data->mfd_cell_size,
+				   NULL, 0, NULL);
+	if (ret)
+		dev_err(&i2c->dev, "Failed to add child devices\n");
+
+	return ret;
 }
 
 static const struct of_device_id simple_mfd_i2c_of_match[] = {

drivers/mfd/simple-mfd-i2c.h

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Simple MFD - I2C
+ *
+ * Author: Lee Jones <lee.jones@linaro.org>
+ *
+ * This driver creates a single register map with the intention for it to be
+ * shared by all sub-devices.  Children can use their parent's device structure
+ * (dev.parent) in order to reference it.
+ *
+ * This driver creates a single register map with the intention for it to be
+ * shared by all sub-devices.  Children can use their parent's device structure
+ * (dev.parent) in order to reference it.
+ *
+ * Once the register map has been successfully initialised, any sub-devices
+ * represented by child nodes in Device Tree or via the MFD cells in the
+ * associated C file will be subsequently registered.
+ */
+
+#ifndef __MFD_SIMPLE_MFD_I2C_H
+#define __MFD_SIMPLE_MFD_I2C_H
+
+#include <linux/mfd/core.h>
+#include <linux/regmap.h>
+
+struct simple_mfd_data {
+	const struct regmap_config *regmap_config;
+	const struct mfd_cell *mfd_cell;
+	size_t mfd_cell_size;
+};
+
+#endif /* __MFD_SIMPLE_MFD_I2C_H */