Re: [RFC PATCH 3/9] net: dsa: hellcreek: Add PTP clock support

On Thu, Jun 18, 2020 at 08:40:23AM +0200, Kurt Kanzenbach wrote:

Why use a spin lock and not a mutex?

 	void __iomem *base;
+	void __iomem *ptp_base;
 	u8 *vidmbrcfg;		/* vidmbrcfg shadow */
+	u64 seconds;		/* PTP seconds */
+	u64 last_ts;		/* Used for overflow detection */
 	size_t fdb_entries;
 };

+static int hellcreek_ptp_gettime(struct ptp_clock_info *ptp,
+				 struct timespec64 *ts)
+{
+	struct hellcreek *hellcreek = ptp_to_hellcreek(ptp);
+	u64 ns;
+
+	spin_lock(&hellcreek->ptp_lock);

Won't a mutex do here instead?

+	ns = __hellcreek_ptp_gettime(hellcreek);
+	spin_unlock(&hellcreek->ptp_lock);
+
+	*ts = ns_to_timespec64(ns);
+
+	return 0;
+}

+static int hellcreek_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
+{
+	struct hellcreek *hellcreek = ptp_to_hellcreek(ptp);
+	u16 negative = 0, counth, countl;
+	u32 count_val;
+
+	/* If the offset is larger than IP-Core slow offset resources. Don't
+	 * concider slow adjustment. Rather, add the offset directly to the

consider

+	 * current time
+	 */
+	if (abs(delta) > MAX_SLOW_OFFSET_ADJ) {
+		struct timespec64 now, then = ns_to_timespec64(delta);
+
+		hellcreek_ptp_gettime(ptp, &now);
+		now = timespec64_add(now, then);
+		hellcreek_ptp_settime(ptp, &now);
+
+		return 0;
+	}
+
+	if (delta < 0) {
+		negative = 1;
+		delta = -delta;
+	}
+
+	/* 'count_val' does not exceed the maximum register size (2^30) */
+	count_val = div_s64(delta, MAX_NS_PER_STEP);
+
+	counth = (count_val & 0xffff0000) >> 16;
+	countl = count_val & 0xffff;
+
+	negative = (negative << 15) & 0x8000;
+
+	spin_lock(&hellcreek->ptp_lock);
+
+	/* Set offset write register */
+	hellcreek_ptp_write(hellcreek, negative, PR_CLOCK_OFFSET_C);
+	hellcreek_ptp_write(hellcreek, MAX_NS_PER_STEP, PR_CLOCK_OFFSET_C);
+	hellcreek_ptp_write(hellcreek, MIN_CLK_CYCLES_BETWEEN_STEPS,
+			    PR_CLOCK_OFFSET_C);
+	hellcreek_ptp_write(hellcreek, countl,  PR_CLOCK_OFFSET_C);
+	hellcreek_ptp_write(hellcreek, counth,  PR_CLOCK_OFFSET_C);
+
+	spin_unlock(&hellcreek->ptp_lock);
+
+	return 0;
+}

+int hellcreek_ptp_setup(struct hellcreek *hellcreek)
+{
+	u16 status;
+
+	/* Set up the overflow work */
+	INIT_DELAYED_WORK(&hellcreek->overflow_work,
+			  hellcreek_ptp_overflow_check);
+
+	/* Setup PTP clock */
+	hellcreek->ptp_clock_info.owner = THIS_MODULE;
+	snprintf(hellcreek->ptp_clock_info.name,
+		 sizeof(hellcreek->ptp_clock_info.name),
+		 dev_name(hellcreek->dev));
+
+	/* IP-Core can add up to 0.5 ns per 8 ns cycle, which means
+	 * accumulator_overflow_rate shall not exceed 62.5 MHz (which adjusts
+	 * the nominal frequency by 6.25%)
+	 */
+	hellcreek->ptp_clock_info.max_adj   = 62500000;
+	hellcreek->ptp_clock_info.n_alarm   = 0;
+	hellcreek->ptp_clock_info.n_pins    = 0;
+	hellcreek->ptp_clock_info.n_ext_ts  = 0;
+	hellcreek->ptp_clock_info.n_per_out = 0;
+	hellcreek->ptp_clock_info.pps	    = 0;
+	hellcreek->ptp_clock_info.adjfine   = hellcreek_ptp_adjfine;
+	hellcreek->ptp_clock_info.adjtime   = hellcreek_ptp_adjtime;
+	hellcreek->ptp_clock_info.gettime64 = hellcreek_ptp_gettime;
+	hellcreek->ptp_clock_info.settime64 = hellcreek_ptp_settime;
+	hellcreek->ptp_clock_info.enable    = hellcreek_ptp_enable;
+
+	hellcreek->ptp_clock = ptp_clock_register(&hellcreek->ptp_clock_info,
+						  hellcreek->dev);
+	if (IS_ERR(hellcreek->ptp_clock))
+		return PTR_ERR(hellcreek->ptp_clock);

The ptp_clock_register() can also return NULL:

 * Returns a valid pointer on success or PTR_ERR on failure.  If PHC
 * support is missing at the configuration level, this function
 * returns NULL, and drivers are expected to gracefully handle that
 * case separately.

+
+	/* Enable the offset correction process, if no offset correction is
+	 * already taking place
+	 */
+	status = hellcreek_ptp_read(hellcreek, PR_CLOCK_STATUS_C);
+	if (!(status & PR_CLOCK_STATUS_C_OFS_ACT))
+		hellcreek_ptp_write(hellcreek,
+				    status | PR_CLOCK_STATUS_C_ENA_OFS,
+				    PR_CLOCK_STATUS_C);
+
+	/* Enable the drift correction process */
+	hellcreek_ptp_write(hellcreek, status | PR_CLOCK_STATUS_C_ENA_DRIFT,
+			    PR_CLOCK_STATUS_C);
+
+	schedule_delayed_work(&hellcreek->overflow_work,
+			      HELLCREEK_OVERFLOW_PERIOD);
+
+	return 0;
+}

Thanks,
Richard