ptp: netc: add the periodic output signal loopback support

The NETC Timer supports looping back the output pulse signal of Fiper-n
into Trigger-n input, so that users can leverage this feature to validate
some other features without external hardware support. For example, users
can use it to test external trigger stamp (EXTTS). And users can combine
EXTTS with loopback mode to check whether the generation time of PPS is
aligned with an integral second of PHC, or the periodic output signal
(PTP_CLK_REQ_PEROUT) whether is generated at the specified time.

Since ptp_clock_info::perout_loopback() has been added to the ptp_clock
driver as a generic interface to enable or disable the periodic output
signal loopback, therefore, netc_timer_perout_loopback() is added as a
callback of ptp_clock_info::perout_loopback().

Test the generation time of PPS event:

$ echo 0 1 > /sys/kernel/debug/ptp0/perout_loopback
$ echo 1 > /sys/class/ptp/ptp0/pps_enable
$ testptp -d /dev/ptp0 -e 3
external time stamp request okay
event index 0 at 63.000000017
event index 0 at 64.000000017
event index 0 at 65.000000017

Test the generation time of the periodic output signal:

$ echo 0 1 > /sys/kernel/debug/ptp0/perout_loopback
$ echo 0 150 0 1 500000000 > /sys/class/ptp/ptp0/period
$ testptp -d /dev/ptp0 -e 3
external time stamp request okay
event index 0 at 150.000000014
event index 0 at 151.500000015
event index 0 at 153.000000014

Signed-off-by: Wei Fang <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/ptp/ptp_netc.c

···
 #define  TMR_ETEP(i)			BIT(8 + (i))
 #define  TMR_COMP_MODE			BIT(15)
 #define  TMR_CTRL_TCLK_PERIOD		GENMASK(25, 16)
+#define  TMR_CTRL_PPL(i)		BIT(27 - (i))
 #define  TMR_CTRL_FS			BIT(28)
 
 #define NETC_TMR_TEVENT			0x0084
···
 	}
 }
 
+static int netc_timer_perout_loopback(struct ptp_clock_info *ptp,
+				      unsigned int index, int on)
+{
+	struct netc_timer *priv = ptp_to_netc_timer(ptp);
+	unsigned long flags;
+	u32 tmr_ctrl;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	tmr_ctrl = netc_timer_rd(priv, NETC_TMR_CTRL);
+	if (on)
+		tmr_ctrl |= TMR_CTRL_PPL(index);
+	else
+		tmr_ctrl &= ~TMR_CTRL_PPL(index);
+
+	netc_timer_wr(priv, NETC_TMR_CTRL, tmr_ctrl);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
 static void netc_timer_adjust_period(struct netc_timer *priv, u64 period)
 {
 	u32 fractional_period = lower_32_bits(period);
···
 	.pps		= 1,
 	.n_per_out	= 3,
 	.n_ext_ts	= 2,
+	.n_per_lp	= 2,
 	.supported_extts_flags = PTP_RISING_EDGE | PTP_FALLING_EDGE |
 				 PTP_STRICT_FLAGS,
 	.adjfine	= netc_timer_adjfine,
···
 	.gettimex64	= netc_timer_gettimex64,
 	.settime64	= netc_timer_settime64,
 	.enable		= netc_timer_enable,
+	.perout_loopback = netc_timer_perout_loopback,
 };
 
 static void netc_timer_init(struct netc_timer *priv)