ptp: Add cycles support for virtual clocks

ptp vclocks require a free running time for their timecounter.
Currently only a physical clock forced to free running is supported.
If vclocks are used, then the physical clock cannot be synchronized
anymore. The synchronized time is not available in hardware in this
case. As a result, timed transmission with TAPRIO hardware support
is not possible anymore.

If hardware would support a free running time additionally to the
physical clock, then the physical clock does not need to be forced to
free running. Thus, the physical clocks can still be synchronized
while vclocks are in use.

The physical clock could be used to synchronize the time domain of the
TSN network and trigger TAPRIO. In parallel vclocks can be used to
synchronize other time domains.

Introduce support for a free running cycle counter called cycles to
physical clocks. Rework ptp vclocks to use this free running cycle
counter. Default implementation is based on time of physical clock.
Thus, behavior of ptp vclocks based on physical clocks without free
running cycle counter is identical to previous behavior.

Signed-off-by: Gerhard Engleder <[e-mail]>
Acked-by: Richard Cochran <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/ptp/ptp_clock.c

···
 {
 	struct ptp_clock *ptp = container_of(pc, struct ptp_clock, clock);
 
-	if (ptp_vclock_in_use(ptp)) {
-		pr_err("ptp: virtual clock in use\n");
+	if (ptp_clock_freerun(ptp)) {
+		pr_err("ptp: physical clock is free running\n");
 		return -EBUSY;
 	}
 
···
 	struct ptp_clock_info *ops;
 	int err = -EOPNOTSUPP;
 
-	if (ptp_vclock_in_use(ptp)) {
-		pr_err("ptp: virtual clock in use\n");
+	if (ptp_clock_freerun(ptp)) {
+		pr_err("ptp: physical clock is free running\n");
 		return -EBUSY;
 	}
 
···
 	kfree(ptp);
 }
 
+static int ptp_getcycles64(struct ptp_clock_info *info, struct timespec64 *ts)
+{
+	if (info->getcyclesx64)
+		return info->getcyclesx64(info, ts, NULL);
+	else
+		return info->gettime64(info, ts);
+}
+
 static void ptp_aux_kworker(struct kthread_work *work)
 {
 	struct ptp_clock *ptp = container_of(work, struct ptp_clock,
···
 	mutex_init(&ptp->pincfg_mux);
 	mutex_init(&ptp->n_vclocks_mux);
 	init_waitqueue_head(&ptp->tsev_wq);
+
+	if (ptp->info->getcycles64 || ptp->info->getcyclesx64) {
+		ptp->has_cycles = true;
+		if (!ptp->info->getcycles64 && ptp->info->getcyclesx64)
+			ptp->info->getcycles64 = ptp_getcycles64;
+	} else {
+		/* Free running cycle counter not supported, use time. */
+		ptp->info->getcycles64 = ptp_getcycles64;
+
+		if (ptp->info->gettimex64)
+			ptp->info->getcyclesx64 = ptp->info->gettimex64;
+
+		if (ptp->info->getcrosststamp)
+			ptp->info->getcrosscycles = ptp->info->getcrosststamp;
+	}
 
 	if (ptp->info->do_aux_work) {
 		kthread_init_delayed_work(&ptp->aux_work, ptp_aux_kworker);

drivers/ptp/ptp_private.h

···
 	int *vclock_index;
 	struct mutex n_vclocks_mux; /* protect concurrent n_vclocks access */
 	bool is_virtual_clock;
+	bool has_cycles;
 };
 
 #define info_to_vclock(d) container_of((d), struct ptp_vclock, info)
···
 	mutex_unlock(&ptp->n_vclocks_mux);
 
 	return in_use;
+}
+
+/* Check if ptp clock shall be free running */
+static inline bool ptp_clock_freerun(struct ptp_clock *ptp)
+{
+	if (ptp->has_cycles)
+		return false;
+
+	return ptp_vclock_in_use(ptp);
 }
 
 extern struct class *ptp_class;

drivers/ptp/ptp_sysfs.c

···
 			*(ptp->vclock_index + ptp->n_vclocks - i) = -1;
 	}
 
-	if (num == 0)
-		dev_info(dev, "only physical clock in use now\n");
-	else
-		dev_info(dev, "guarantee physical clock free running\n");
+	/* Need to inform about changed physical clock behavior */
+	if (!ptp->has_cycles) {
+		if (num == 0)
+			dev_info(dev, "only physical clock in use now\n");
+		else
+			dev_info(dev, "guarantee physical clock free running\n");
+	}
 
 	ptp->n_vclocks = num;
 	mutex_unlock(&ptp->n_vclocks_mux);

drivers/ptp/ptp_vclock.c

···
 	int err;
 	u64 ns;
 
-	err = pptp->info->gettimex64(pptp->info, &pts, sts);
+	err = pptp->info->getcyclesx64(pptp->info, &pts, sts);
 	if (err)
 		return err;
 
···
 	int err;
 	u64 ns;
 
-	err = pptp->info->getcrosststamp(pptp->info, xtstamp);
+	err = pptp->info->getcrosscycles(pptp->info, xtstamp);
 	if (err)
 		return err;
 
···
 	struct ptp_clock *ptp = vclock->pclock;
 	struct timespec64 ts = {};
 
-	if (ptp->info->gettimex64)
-		ptp->info->gettimex64(ptp->info, &ts, NULL);
-	else
-		ptp->info->gettime64(ptp->info, &ts);
+	ptp->info->getcycles64(ptp->info, &ts);
 
 	return timespec64_to_ns(&ts);
 }
···
 
 	vclock->pclock = pclock;
 	vclock->info = ptp_vclock_info;
-	if (pclock->info->gettimex64)
+	if (pclock->info->getcyclesx64)
 		vclock->info.gettimex64 = ptp_vclock_gettimex;
 	else
 		vclock->info.gettime64 = ptp_vclock_gettime;
-	if (pclock->info->getcrosststamp)
+	if (pclock->info->getcrosscycles)
 		vclock->info.getcrosststamp = ptp_vclock_getcrosststamp;
 	vclock->cc = ptp_vclock_cc;
 

include/linux/ptp_clock_kernel.h

···
  * @settime64:  Set the current time on the hardware clock.
  *              parameter ts: Time value to set.
  *
+ * @getcycles64:  Reads the current free running cycle counter from the hardware
+ *                clock.
+ *                If @getcycles64 and @getcyclesx64 are not supported, then
+ *                @gettime64 or @gettimex64 will be used as default
+ *                implementation.
+ *                parameter ts: Holds the result.
+ *
+ * @getcyclesx64:  Reads the current free running cycle counter from the
+ *                 hardware clock and optionally also the system clock.
+ *                 If @getcycles64 and @getcyclesx64 are not supported, then
+ *                 @gettimex64 will be used as default implementation if
+ *                 available.
+ *                 parameter ts: Holds the PHC timestamp.
+ *                 parameter sts: If not NULL, it holds a pair of timestamps
+ *                 from the system clock. The first reading is made right before
+ *                 reading the lowest bits of the PHC timestamp and the second
+ *                 reading immediately follows that.
+ *
+ * @getcrosscycles:  Reads the current free running cycle counter from the
+ *                   hardware clock and system clock simultaneously.
+ *                   If @getcycles64 and @getcyclesx64 are not supported, then
+ *                   @getcrosststamp will be used as default implementation if
+ *                   available.
+ *                   parameter cts: Contains timestamp (device,system) pair,
+ *                   where system time is realtime and monotonic.
+ *
  * @enable:   Request driver to enable or disable an ancillary feature.
  *            parameter request: Desired resource to enable or disable.
  *            parameter on: Caller passes one to enable or zero to disable.
···
 	int (*getcrosststamp)(struct ptp_clock_info *ptp,
 			      struct system_device_crosststamp *cts);
 	int (*settime64)(struct ptp_clock_info *p, const struct timespec64 *ts);
+	int (*getcycles64)(struct ptp_clock_info *ptp, struct timespec64 *ts);
+	int (*getcyclesx64)(struct ptp_clock_info *ptp, struct timespec64 *ts,
+			    struct ptp_system_timestamp *sts);
+	int (*getcrosscycles)(struct ptp_clock_info *ptp,
+			      struct system_device_crosststamp *cts);
 	int (*enable)(struct ptp_clock_info *ptp,
 		      struct ptp_clock_request *request, int on);
 	int (*verify)(struct ptp_clock_info *ptp, unsigned int pin,