[PATCH] i2ctransfer: Print modifier flags in PRINT_HEADER

[PATCH] i2ctransfer: Print modifier flags in PRINT_HEADER

[Benoît Monin]

Print the optional message modifier flags when printing the message
header. For example:

    i2ctransfer -v -y 3 pr1@0x33 itr1@0x33
    msg 0: addr 0x33, read, len 1, emit STOP, buf 0x10
    msg 1: addr 0x33, read, len 1, ignore NACK, toggle read/write bit, buf 0x10

If no optional flag is set, the output is unchanged.

Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
---
 tools/i2ctransfer.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/i2ctransfer.c b/tools/i2ctransfer.c
index a49b734..0a310a7 100644
--- a/tools/i2ctransfer.c
+++ b/tools/i2ctransfer.c
@@ -123,6 +123,26 @@ static void print_msgs(struct i2c_msg *msgs, __u32 nmsgs, unsigned int flags)
 				fprintf(output, "%u", len);
 			else
 				fprintf(output, "TBD");
+#ifdef I2C_M_IGNORE_NAK
+			if (msgs[i].flags & I2C_M_IGNORE_NAK)
+				fprintf(output, ", ignore NACK");
+#endif
+#ifdef I2C_M_NO_RD_ACK
+			if (msgs[i].flags & I2C_M_NO_RD_ACK)
+				fprintf(output, ", no master ACK/NACK bit");
+#endif
+#ifdef I2C_M_STOP
+			if (msgs[i].flags & I2C_M_STOP)
+				fprintf(output, ", emit STOP");
+#endif
+#ifdef I2C_M_NOSTART
+			if (msgs[i].flags & I2C_M_NOSTART)
+				fprintf(output, ", skip repeated start");
+#endif
+#ifdef I2C_M_REV_DIR_ADDR
+			if (msgs[i].flags & I2C_M_REV_DIR_ADDR)
+				fprintf(output, ", toggle read/write bit");
+#endif
 		}
 
 		if (len && print_buf) {

---
base-commit: 5852f5375eea6ca9dabf31f4772cb8b8ecc905d8
change-id: 20260706-print-header-flags-e841fc4398ed

Best regards,
--  
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH] i2ctransfer: Print modifier flags in PRINT_HEADER

[Wolfram Sang]

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On Mon, Jul 06, 2026 at 03:18:46PM +0200, Benoît Monin wrote:
> Print the optional message modifier flags when printing the message
> header. For example:
> 
>     i2ctransfer -v -y 3 pr1@0x33 itr1@0x33
>     msg 0: addr 0x33, read, len 1, emit STOP, buf 0x10
>     msg 1: addr 0x33, read, len 1, ignore NACK, toggle read/write bit, buf 0x10
> 
> If no optional flag is set, the output is unchanged.
> 
> Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>

Applied, thanks!


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