(This is 2nd version of SCCB helpers patch. After 1st version was
submitted, I sent alternative patch titled "i2c: add I2C_M_FORCE_STOP".
But it wasn't accepted because it makes the I2C core code unreadable.
I couldn't find out a way to untangle it, so I returned to the original
approach.)
This adds Serial Camera Control Bus (SCCB) helper functions (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 functions in order to make it work
with most i2c controllers.
As the ov772x device doesn't support repeated starts, this driver currently
requires I2C_FUNC_PROTOCOL_MANGLING that is not supported by many i2c
controller drivers.
With the sccb_read_byte() that issues two separated requests in order to
avoid repeated start, the driver doesn't require I2C_FUNC_PROTOCOL_MANGLING.
Cc: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxxxx>
Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx>
Cc: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Cc: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
---
* v2
- Convert all helpers into static inline functions, and remove C source
and Kconfig option.
- Acquire i2c adapter lock while issuing two requests for sccb_read_byte
drivers/media/i2c/sccb.h | 74 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 74 insertions(+)
create mode 100644 drivers/media/i2c/sccb.h
diff --git a/drivers/media/i2c/sccb.h b/drivers/media/i2c/sccb.h
new file mode 100644
index 0000000..a531fdc
--- /dev/null
+++ b/drivers/media/i2c/sccb.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Serial Camera Control Bus (SCCB) helper functions
+ */
+
+#ifndef __SCCB_H__
+#define __SCCB_H__
+
+#include <linux/i2c.h>
+
+/**
+ * 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)
+{
+ u8 val;
+ struct i2c_msg msg[] = {
+ {
+ .addr = client->addr,
+ .len = 1,
+ .buf = &addr,
+ },
+ {
+ .addr = client->addr,
+ .flags = I2C_M_RD,
+ .len = 1,
+ .buf = &val,
+ },
+ };
+ int ret;
+ int i;
+
+ i2c_lock_adapter(client->adapter);
+
+ /* Issue two separated requests in order to avoid repeated start */
+ for (i = 0; i < 2; i++) {
+ ret = __i2c_transfer(client->adapter, &msg[i], 1);
+ if (ret != 1)
+ break;
+ }
+
+ i2c_unlock_adapter(client->adapter);
+
+ return i == 2 ? val : ret;
+}
+
+/**
+ * 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)
+{
+ int ret;
+ unsigned char msgbuf[] = { addr, data };
+
+ ret = i2c_master_send(client, msgbuf, 2);
+ if (ret < 0)
+ return ret;
+
+ return 0;
+}
+
+#endif /* __SCCB_H__ */
--
2.7.4
