ptp: Add .getmaxphase callback to ptp_clock_info

Enables advertisement of the maximum offset supported by the phase control
functionality of PHCs. The callback is used to return an error if an offset
not supported by the PHC is used in ADJ_OFFSET. The ioctls
PTP_CLOCK_GETCAPS and PTP_CLOCK_GETCAPS2 now advertise the maximum offset a
PHC's phase control functionality is capable of supporting. Introduce new
sysfs node, max_phase_adjustment.

Cc: Jakub Kicinski <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Richard Cochran <[e-mail]>
Cc: Maciek Machnikowski <[e-mail]>
Signed-off-by: Rahul Rameshbabu <[e-mail]>
Acked-by: Richard Cochran <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/ptp/ptp_chardev.c

···
 		caps.pps = ptp->info->pps;
 		caps.n_pins = ptp->info->n_pins;
 		caps.cross_timestamping = ptp->info->getcrosststamp != NULL;
-		caps.adjust_phase = ptp->info->adjphase != NULL;
+		caps.adjust_phase = ptp->info->adjphase != NULL &&
+				    ptp->info->getmaxphase != NULL;
+		if (caps.adjust_phase)
+			caps.max_phase_adj = ptp->info->getmaxphase(ptp->info);
 		if (copy_to_user((void __user *)arg, &caps, sizeof(caps)))
 			err = -EFAULT;
 		break;

drivers/ptp/ptp_clock.c

···
 		ptp->dialed_frequency = tx->freq;
 	} else if (tx->modes & ADJ_OFFSET) {
 		if (ops->adjphase) {
+			s32 max_phase_adj = ops->getmaxphase(ops);
 			s32 offset = tx->offset;
 
 			if (!(tx->modes & ADJ_NANO))
 				offset *= NSEC_PER_USEC;
+
+			if (offset > max_phase_adj || offset < -max_phase_adj)
+				return -ERANGE;
 
 			err = ops->adjphase(ops, offset);
 		}

drivers/ptp/ptp_sysfs.c

···
 }
 static DEVICE_ATTR_RO(clock_name);
 
+static ssize_t max_phase_adjustment_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *page)
+{
+	struct ptp_clock *ptp = dev_get_drvdata(dev);
+
+	return snprintf(page, PAGE_SIZE - 1, "%d\n",
+			ptp->info->getmaxphase(ptp->info));
+}
+static DEVICE_ATTR_RO(max_phase_adjustment);
+
 #define PTP_SHOW_INT(name, var)						\
 static ssize_t var##_show(struct device *dev,				\
 			   struct device_attribute *attr, char *page)	\
···
 	&dev_attr_clock_name.attr,
 
 	&dev_attr_max_adjustment.attr,
+	&dev_attr_max_phase_adjustment.attr,
 	&dev_attr_n_alarms.attr,
 	&dev_attr_n_external_timestamps.attr,
 	&dev_attr_n_periodic_outputs.attr,

include/linux/ptp_clock_kernel.h

···
  *             parameter delta: PHC servo phase adjustment target
  *                              in nanoseconds.
  *
+ * @getmaxphase:  Advertises maximum offset that can be provided
+ *                to the hardware clock's phase control functionality
+ *                through adjphase.
+ *
  * @adjtime:  Shifts the time of the hardware clock.
  *            parameter delta: Desired change in nanoseconds.
  *
···
 	struct ptp_pin_desc *pin_config;
 	int (*adjfine)(struct ptp_clock_info *ptp, long scaled_ppm);
 	int (*adjphase)(struct ptp_clock_info *ptp, s32 phase);
+	s32 (*getmaxphase)(struct ptp_clock_info *ptp);
 	int (*adjtime)(struct ptp_clock_info *ptp, s64 delta);
 	int (*gettime64)(struct ptp_clock_info *ptp, struct timespec64 *ts);
 	int (*gettimex64)(struct ptp_clock_info *ptp, struct timespec64 *ts,

include/uapi/linux/ptp_clock.h

···
 	int cross_timestamping;
 	/* Whether the clock supports adjust phase */
 	int adjust_phase;
-	int rsv[12];   /* Reserved for future use. */
+	int max_phase_adj; /* Maximum phase adjustment in nanoseconds. */
+	int rsv[11];       /* Reserved for future use. */
 };
 
 struct ptp_extts_request {

tools/testing/selftests/ptp/testptp.c

···
 			       "  %d pulse per second\n"
 			       "  %d programmable pins\n"
 			       "  %d cross timestamping\n"
-			       "  %d adjust_phase\n",
+			       "  %d adjust_phase\n"
+			       "  %d maximum phase adjustment (ns)\n",
 			       caps.max_adj,
 			       caps.n_alarm,
 			       caps.n_ext_ts,
···
 			       caps.pps,
 			       caps.n_pins,
 			       caps.cross_timestamping,
-			       caps.adjust_phase);
+			       caps.adjust_phase,
+			       caps.max_phase_adj);
 		}
 	}