renesas: reject PTP_STRICT_FLAGS as unsupported

The ravb_ptp_extts() function checks the flags coming from the
PTP_EXTTS_REQUEST ioctl, to ensure that future flags are not accepted on
accident.

This was updated to 'honor' the PTP_STRICT_FLAGS in commit 6138e68
("ptp: Introduce strict checking of external time stamp options.").
However, the driver does not *actually* validate the flags.

I originally fixed this driver to reject future flags in commit
592025a ("renesas: reject unsupported external timestamp flags"). It
is still unclear whether this hardware timestamps the rising, falling, or
both edges of the input signal.

Accepting requests with PTP_STRICT_FLAGS is a bug, as this could lead to
users mistakenly assuming a request with PTP_RISING_EDGE actually
timestamps the rising edge only.

Reject requests with PTP_STRICT_FLAGS (and hence all PTP_EXTTS_REQUEST2
requests) until someone with access to the datasheet or hardware knowledge
can confirm the timestamping behavior and update this driver.

Fixes: 6138e68 ("ptp: Introduce strict checking of external time stamp options.")
Signed-off-by: Jacob Keller <[email protected]>
Reviewed-by: Niklas Söderlund <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/20250312-jk-net-fixes-supported-extts-flags-v2-2-ea930ba82459@intel.com
Signed-off-by: Paolo Abeni <[email protected]>

Author: jacob-keller

drivers/net/ethernet/renesas/ravb_ptp.c

@@ -179,8 +179,7 @@ static int ravb_ptp_extts(struct ptp_clock_info *ptp,
 	/* Reject requests with unsupported flags */
 	if (req->flags & ~(PTP_ENABLE_FEATURE |
 			   PTP_RISING_EDGE |
-			   PTP_FALLING_EDGE |
-			   PTP_STRICT_FLAGS))
+			   PTP_FALLING_EDGE))
 		return -EOPNOTSUPP;
 
 	if (req->index)