[U-Boot] [PATCH] soft_i2c.c add option for repeated start in i2c_read()

Andrew Dyer
2008-12-29T23:36:01Z

This patch adds a #define to optionally change the behaviour of
i2c_read() in soft_i2c.c to send an I2C repeated start instead of a
stop-start between sending the device address pointer write and
reading back the data. The current behaviour is retained as the
default.

While most devices will work either way, I have a smart battery(*) that
requires repeated start, and someone at some point found a device that
required a stop-start.

(*) http://www.inspired-energy.com/Standard_Products/NL2054/NL2054%20Rev1.0%20Data%20Sheet.pdf

Signed-off-by: Andrew Dyer <adyer@righthandtech.com>
---
README | 9 +++++++++
drivers/i2c/soft_i2c.c | 12 +++++++++++-
2 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/README b/README
index 2a553c2..763fb7a 100644
--- a/README
+++ b/README
@@ -1496,6 +1496,15 @@ The following options need to be configured:
Bus on the MPC8260. But it should be not so difficult
to add this option to other architectures.

+ CONFIG_SOFT_I2C_READ_REPEATED_START
+
+ defining this will force the i2c_read() function in
+ the soft_i2c driver to perform an I2C repeated start
+ between writing the address pointer and reading the
+ data. If this define is omitted the default behaviour
+ of doing a stop-start sequence will be used. Most I2C
+ devices can use either method, but some require one or
+ the other.

- SPI Support: CONFIG_SPI

diff --git a/drivers/i2c/soft_i2c.c b/drivers/i2c/soft_i2c.c
index a27de5a..da6cec1 100644
--- a/drivers/i2c/soft_i2c.c
+++ b/drivers/i2c/soft_i2c.c
@@ -385,8 +385,18 @@ int i2c_read(uchar chip, uint addr, int alen, uchar *buffer, int len)
}
shift -= 8;
}
- send_stop(); /* reportedly some chips need a full stop */
+
+ /* Some I2C chips need a stop/start sequence here,
+ * other chips don't work with a full stop and need
+ * only a start. Default behaviour is to send the
+ * stop/start sequence.
+ */
+#ifdef CONFIG_SOFT_I2C_READ_REPEATED_START
send_start();
+#else
+ send_stop();
+ send_start();
+#endif
}
/*
* Send the chip address again, this time for a read cycle.
--
1.5.6.3