ptp: Allow exposing cycles only for clocks with free-running counter

The PTP core falls back to gettimex64 and getcrosststamp when
getcycles64 or getcyclesx64 are not implemented. This causes the CYCLES
ioctls to retrieve PHC real time instead of free-running cycles.

Reject PTP_SYS_OFFSET_{PRECISE,EXTENDED}_CYCLES for clocks without
free-running counter support since the result would represent PHC real
time and system time rather than cycles and system time.

Fixes: faf23f5 ("ptp: Add ioctl commands to expose raw cycle counter values")
Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20251029083813.2276997-1-cjubran@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: cjubran

drivers/ptp/ptp_chardev.c

@@ -561,10 +561,14 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd,
 		return ptp_mask_en_single(pccontext->private_clkdata, argptr);
 
 	case PTP_SYS_OFFSET_PRECISE_CYCLES:
+		if (!ptp->has_cycles)
+			return -EOPNOTSUPP;
 		return ptp_sys_offset_precise(ptp, argptr,
 					      ptp->info->getcrosscycles);
 
 	case PTP_SYS_OFFSET_EXTENDED_CYCLES:
+		if (!ptp->has_cycles)
+			return -EOPNOTSUPP;
 		return ptp_sys_offset_extended(ptp, argptr,
 					       ptp->info->getcyclesx64);
 	default: