[PATCH -next v3 1/2] i2c: add SCCB helpers

[Akinobu Mita <akinobu.mita@gmail.com>]

This adds Serial Camera Control Bus (SCCB) helpers (sccb_is_available,
sccb_read_byte, and sccb_write_byte) that are intended to be used by some
of Omnivision sensor drivers.

The ov772x driver is going to use these helpers.

It was previously only worked with the i2c controller drivers that support
I2C_FUNC_PROTOCOL_MANGLING, because the ov772x device doesn't support
repeated starts.  After commit 0b964d183cbf ("media: ov772x: allow i2c
controllers without I2C_FUNC_PROTOCOL_MANGLING"), reading ov772x register
is replaced with issuing two separated i2c messages in order to avoid
repeated start.  Using SCCB helpers hides the implementation detail.

Cc: Peter Rosin <peda@axentia.se>
Cc: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 include/linux/i2c-sccb.h | 77 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 include/linux/i2c-sccb.h

diff --git a/include/linux/i2c-sccb.h b/include/linux/i2c-sccb.h
new file mode 100644
index 0000000..61dece9
--- /dev/null
+++ b/include/linux/i2c-sccb.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Serial Camera Control Bus (SCCB) helper functions
+ */
+
+#ifndef _LINUX_I2C_SCCB_H
+#define _LINUX_I2C_SCCB_H
+
+#include <linux/i2c.h>
+
+/**
+ * sccb_is_available - Check if the adapter supports SCCB protocol
+ * @adap: I2C adapter
+ *
+ * Return true if the I2C adapter is capable of using SCCB helper functions,
+ * false otherwise.
+ */
+static inline bool sccb_is_available(struct i2c_adapter *adap)
+{
+	u32 needed_funcs = I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_WRITE_BYTE_DATA;
+
+#if 0
+	/*
+	 * sccb_xfer not needed yet, since there is no driver support currently.
+	 * Just showing how it should be done if we ever need it.
+	 */
+	if (adap->algo->sccb_xfer)
+		return true;
+#endif
+
+	return (i2c_get_functionality(adap) & needed_funcs) == needed_funcs;
+}
+
+/**
+ * sccb_read_byte - Read data from SCCB slave device
+ * @client: Handle to slave device
+ * @addr: Register to be read from
+ *
+ * This executes the 2-phase write transmission cycle that is followed by a
+ * 2-phase read transmission cycle, returning negative errno else a data byte
+ * received from the device.
+ */
+static inline int sccb_read_byte(struct i2c_client *client, u8 addr)
+{
+	int ret;
+	union i2c_smbus_data data;
+
+	i2c_lock_bus(client->adapter, I2C_LOCK_SEGMENT);
+
+	ret = __i2c_smbus_xfer(client->adapter, client->addr, client->flags,
+				I2C_SMBUS_WRITE, addr, I2C_SMBUS_BYTE, NULL);
+	if (ret < 0)
+		goto out;
+
+	ret = __i2c_smbus_xfer(client->adapter, client->addr, client->flags,
+				I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &data);
+out:
+	i2c_unlock_bus(client->adapter, I2C_LOCK_SEGMENT);
+
+	return ret < 0 ? ret : data.byte;
+}
+
+/**
+ * sccb_write_byte - Write data to SCCB slave device
+ * @client: Handle to slave device
+ * @addr: Register to write to
+ * @data: Value to be written
+ *
+ * This executes the SCCB 3-phase write transmission cycle, returning negative
+ * errno else zero on success.
+ */
+static inline int sccb_write_byte(struct i2c_client *client, u8 addr, u8 data)
+{
+	return i2c_smbus_write_byte_data(client, addr, data);
+}
+
+#endif /* _LINUX_I2C_SCCB_H */
-- 
2.7.4