[U-Boot] [PATCH V2] cmd_i2c: Provide option for bulk 'i2c write' in one transaction

[Lubomir Popov]

I2C chips do exist that require a write of some multi-byte data to occur in
a single bus transaction (aka atomic transfer), otherwise either the write
does not come into effect at all, or normal operation of internal circuitry
cannot be guaranteed. The current implementation of the 'i2c write' command
(transfer of multiple bytes from a memory buffer) in fact performs a separate
transaction for each byte to be written and thus cannot support such types of
I2C slave devices.

This patch provides an alternative by allowing 'i2c write' to execute the
write transfer of the given number of bytes in a single bus transaction if
the '-s' option is specified as a final command argument. Else the current
re-addressing method is used.

Signed-off-by: Lubomir Popov <l-popov at ti.com>
---
Changes in V2:
The option to use bulk transfer vs re-addressing is implemented as a run-time
command argument and shall better fit into the new I2C DM (thanks to Simon for
the hint). V1 used conditional compilation through a board header definition.

 common/cmd_i2c.c |   35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/common/cmd_i2c.c b/common/cmd_i2c.c
index c266b88..5cb7dca 100644
--- a/common/cmd_i2c.c
+++ b/common/cmd_i2c.c
@@ -270,7 +270,7 @@ static int do_i2c_write(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[
 	uint	devaddr, alen, length;
 	u_char  *memaddr;

-	if (argc != 5)
+	if ((argc < 5) || (argc > 6))
 		return cmd_usage(cmdtp);

 	/*
@@ -293,20 +293,34 @@ static int do_i2c_write(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[
 		return cmd_usage(cmdtp);

 	/*
-	 * Length is the number of objects, not number of bytes.
+	 * Length is the number of bytes.
 	 */
 	length = simple_strtoul(argv[4], NULL, 16);
-
-	while (length-- > 0) {
-		if (i2c_write(chip, devaddr++, alen, memaddr++, 1) != 0) {
+
+	if (argc == 6 && !strcmp(argv[5], "-s")) {
+		/*
+		 * Write all bytes in a single I2C transaction. If the target
+		 * device is an EEPROM, it is your responsibility to not cross
+		 * a page boundary. No write delay upon completion, take this
+		 * into account if linking commands.
+		 */
+		if (i2c_write(chip, devaddr, alen, memaddr, length) != 0)
 			return i2c_report_err(-1, I2C_ERR_WRITE);
-		}
+	} else {
+		/*
+		 * Repeated addressing - perform <length> separate
+		 * write transactions of one byte each
+		 */
+		while (length-- > 0) {
+			if (i2c_write(chip, devaddr++, alen, memaddr++, 1) != 0)
+				return i2c_report_err(-1, I2C_ERR_WRITE);
 /*
  * No write delay with FRAM devices.
  */
 #if !defined(CONFIG_SYS_I2C_FRAM)
-		udelay(11000);
+			udelay(11000);
 #endif
+		}
 	}
 	return 0;
 }
@@ -1559,7 +1573,7 @@ static cmd_tbl_t cmd_i2c_sub[] = {
 	U_BOOT_CMD_MKENT(nm, 2, 1, do_i2c_nm, "", ""),
 	U_BOOT_CMD_MKENT(probe, 0, 1, do_i2c_probe, "", ""),
 	U_BOOT_CMD_MKENT(read, 5, 1, do_i2c_read, "", ""),
-	U_BOOT_CMD_MKENT(write, 5, 0, do_i2c_write, "", ""),
+	U_BOOT_CMD_MKENT(write, 6, 0, do_i2c_write, "", ""),
 	U_BOOT_CMD_MKENT(reset, 0, 1, do_i2c_reset, "", ""),
 #if defined(CONFIG_CMD_SDRAM)
 	U_BOOT_CMD_MKENT(sdram, 1, 1, do_sdram, "", ""),
@@ -1623,7 +1637,8 @@ static char i2c_help_text[] =
 	"i2c nm chip address[.0, .1, .2] - write to I2C device (constant address)\n"
 	"i2c probe [address] - test for and show device(s) on the I2C bus\n"
 	"i2c read chip address[.0, .1, .2] length memaddress - read to memory \n"
-	"i2c write memaddress chip address[.0, .1, .2] length - write memory to i2c\n"
+	"i2c write memaddress chip address[.0, .1, .2] length [-s] - write memory\n"
+	"          to I2C; the -s option selects bulk write in a single transaction\n"
 	"i2c reset - re-init the I2C Controller\n"
 #if defined(CONFIG_CMD_SDRAM)
 	"i2c sdram chip - print SDRAM configuration information\n"
@@ -1632,7 +1647,7 @@ static char i2c_help_text[] =
 #endif

 U_BOOT_CMD(
-	i2c, 6, 1, do_i2c,
+	i2c, 7, 1, do_i2c,
 	"I2C sub-system",
 	i2c_help_text
 );
-- 
1.7.9.5