regmap: implement regmap_init_i2c

Linux offers a helper for creating regmaps over i2c. Add a similar
helper for barebox to ease driver porting.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210531072406.5630-2-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

2 files changed, 45 insertions, 0 deletions

diff --git a/drivers/base/regmap/Makefile b/drivers/base/regmap/Makefile
index ab2387037d..b12b695311 100644
--- a/drivers/base/regmap/Makefile
+++ b/drivers/base/regmap/Makefile
@@ -1,2 +1,3 @@
 obj-y	+= regmap.o
 obj-y	+= regmap-mmio.o
+obj-$(CONFIG_I2C)	+= regmap-i2c.o
diff --git a/drivers/base/regmap/regmap-i2c.c b/drivers/base/regmap/regmap-i2c.c
new file mode 100644
index 0000000000..88b24ae6a8
--- /dev/null
+++ b/drivers/base/regmap/regmap-i2c.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2021, Ahmad Fatoum, Pengutronix
+ */
+
+#include <i2c/i2c.h>
+#include <regmap.h>
+
+
+static int regmap_i2c_reg_read(void *client, unsigned int reg, unsigned int *val)
+{
+	u8 buf[1];
+	int ret;
+
+	ret = i2c_read_reg(client, reg, buf, 1);
+	if (ret != 1)
+		return ret;
+
+	*val = buf[0];
+	return 0;
+}
+
+static int regmap_i2c_reg_write(void *client, unsigned int reg, unsigned int val)
+{
+	u8 buf[] = { val & 0xff };
+	int ret;
+
+	ret = i2c_write_reg(client, reg, buf, 1);
+	if (ret != 1)
+		return ret;
+
+	return 0;
+}
+
+static const struct regmap_bus regmap_regmap_i2c_bus = {
+	.reg_write = regmap_i2c_reg_write,
+	.reg_read = regmap_i2c_reg_read,
+};
+
+struct regmap *regmap_init_i2c(struct i2c_client *client,
+			       const struct regmap_config *config)
+{
+	return  regmap_init(&client->dev, &regmap_regmap_i2c_bus, client, config);
+}