[PATCH i2c-tools v2 2/2] i2ctransfer: Add optional message modifier flags

["Benoît Monin" <benoit.monin@bootlin.com>]

Allow setting protocol mangling and repeated start elision flags of an i2c
message with a set of optional command-line flags. These optional flags
are parsed at the beginning of the DESC field up to a read or write flag.

For example, to read one byte from address 0x50 followed by a stop, then
write two bytes at 0x54 on bus 0, one would call i2ctransfer as follow:

    i2ctransfer 0 pr1@0x50 w2@0x54 0x10 0x20

Since the new flags are optional, this patch preserves the compatibility
of the i2ctransfer syntax.

Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
---
 tools/i2ctransfer.8 | 26 +++++++++++++++++++++++++-
 tools/i2ctransfer.c | 34 +++++++++++++++++++++++++---------
 2 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/tools/i2ctransfer.8 b/tools/i2ctransfer.8
index 4bdf436..45c744d 100644
--- a/tools/i2ctransfer.8
+++ b/tools/i2ctransfer.8
@@ -96,8 +96,11 @@ The number of blocks is limited by the Linux Kernel and defined by I2C_RDWR_IOCT
 .I desc
 blocks are composed like this:
 
-.I {r|w}<length_of_message>[@address]
+.I [inpst]{r|w}<length_of_message>[@address]
 
+.TP
+.B [inpst]
+specifies optional MESSAGE MODIFIER FLAGS. See the section below for details.
 .TP
 .B {r|w}
 specifies if the message is read or write
@@ -141,6 +144,27 @@ decrease value by 1 until end of message (i.e. 0xff- means 0xff, 0xfe, 0xfd, ...
 p
 use value as seed for an 8 bit pseudo random sequence (i.e. 0p means 0x00, 0x50, 0xb0, ...)
 
+.SH "MESSAGE MODIFIER FLAGS"
+.PP
+These optional flags can be used to change the handling of a message when it is sent on the bus.
+Note that not all flags (or any) may be supported by your particular hardware.
+
+.TP
+.B i
+ignore NACK from client, treat them as ACK.
+.TP
+.B n
+in a read message, master ACK/NACK bit is skipped.
+.TP
+.B p
+emit a STOP after the message.
+.TP
+.B s
+skip repeated start.
+.TP
+.B t
+toggle read/write bit.
+
 .SH EXAMPLES
 .PP
 On bus 0, from an EEPROM at address 0x50, read 8 byte from offset 0x64
diff --git a/tools/i2ctransfer.c b/tools/i2ctransfer.c
index 4db98e3..921ffaa 100644
--- a/tools/i2ctransfer.c
+++ b/tools/i2ctransfer.c
@@ -52,9 +52,16 @@ static void help(void)
 		"           -V version info\n"
 		"           -y yes to all confirmations\n"
 		"  I2CBUS is an integer or an I2C bus name\n"
-		"  DESC describes the transfer in the form: {r|w}LENGTH[@address]\n"
-		"    1) read/write-flag 2) LENGTH (range 0-65535, or '?')\n"
-		"    3) I2C address (use last one if omitted)\n"
+		"  DESC describes the transfer in the form: [inpst]{r|w}LENGTH[@address]\n"
+		"    1) optional message modifier flags\n"
+		"       i: ignore NACK from client\n"
+		"       n: no master ACK/NACK bit in a read message\n"
+		"       p: emit a STOP after the message\n"
+		"       s: skip repeated start\n"
+		"       t: toggle read/write bit\n"
+		"    2) mandatory read/write flag\n"
+		"    3) LENGTH (range 0-65535, or '?')\n"
+		"    4) I2C address (use last one if omitted)\n"
 		"  DATA are LENGTH bytes for a write message. They can be shortened by a suffix:\n"
 		"    = (keep value constant until LENGTH)\n"
 		"    + (increase value by 1 until LENGTH)\n"
@@ -202,12 +209,21 @@ int main(int argc, char *argv[])
 		case PARSE_GET_DESC:
 			flags = 0;
 
-			switch (*arg_ptr++) {
-			case 'r': flags |= I2C_M_RD; break;
-			case 'w': break;
-			default:
-				fprintf(stderr, "Error: Invalid direction\n");
-				goto err_out_with_arg;
+			for (int done = 0; !done; ) {
+				switch (*arg_ptr++) {
+				/* optional flags */
+				case 'i': flags |= I2C_M_IGNORE_NAK; break;
+				case 'n': flags |= I2C_M_NO_RD_ACK; break;
+				case 'p': flags |= I2C_M_STOP; break;
+				case 's': flags |= I2C_M_NOSTART; break;
+				case 't': flags |= I2C_M_REV_DIR_ADDR; break;
+				/* mandatory flags */
+				case 'r': flags |= I2C_M_RD; done = 1; break;
+				case 'w': done = 1; break;
+				default:
+					fprintf(stderr, "Error: Invalid flag\n");
+					goto err_out_with_arg;
+				}
 			}
 
 			if (*arg_ptr == '?') {

-- 
2.52.0