soft_i2c.c add option for repeated start in i2c_read()

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

---
 README                 |    9 +++++++++
 drivers/i2c/soft_i2c.c |   12 +++++++++++-
 2 files changed, 20 insertions(+), 1 deletions(-)

index 2a553c2..763fb7a 100644
@@ -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
 

index a27de5a..da6cec1 100644
@@ -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

Dear Andrew Dyer,

Applied, thanks.

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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