-----Original Message-----
From: Richard Cochran <richardcochran@gmail.com>
Sent: Tuesday, March 24, 2020 9:08 PM
To: Y.b. Lu <yangbo.lu@nxp.com>
Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org; David S . Miller
[off-list ref]; Vladimir Oltean [off-list ref];
Claudiu Manoil [off-list ref]; Andrew Lunn [off-list ref];
Vivien Didelot [off-list ref]; Florian Fainelli
[off-list ref]; Alexandre Belloni [off-list ref];
Microchip Linux Driver Support [off-list ref]
Subject: Re: [PATCH 6/6] ptp_ocelot: support 4 programmable pins

On Fri, Mar 20, 2020 at 06:37:26PM +0800, Yangbo Lu wrote:

quoted

+static int ocelot_ptp_enable(struct ptp_clock_info *ptp,
+			     struct ptp_clock_request *rq, int on)
+{
+	struct ocelot *ocelot = container_of(ptp, struct ocelot, ptp_info);
+	enum ocelot_ptp_pins ptp_pin;
+	struct timespec64 ts;
+	unsigned long flags;
+	int pin = -1;
+	u32 val;
+	s64 ns;
+
+	switch (rq->type) {
+	case PTP_CLK_REQ_PEROUT:
+		/* Reject requests with unsupported flags */
+		if (rq->perout.flags)
+			return -EOPNOTSUPP;
+
+		/*
+		 * TODO: support disabling function
+		 * When ptp_disable_pinfunc() is to disable function,
+		 * it has already held pincfg_mux.
+		 * However ptp_find_pin() in .enable() called also needs
+		 * to hold pincfg_mux.
+		 * This causes dead lock. So, just return for function
+		 * disabling, and this needs fix-up.

What dead lock?

When enable(PTP_CLK_REQ_PEROUT, on=0) is called, you don't need to
call ptp_disable_pinfunc().  Just stop the periodic waveform
generator.  The assignment of function to pin remains unchanged.

This happens when we try to change pin function through ptp_ioctl PTP_PIN_SETFUNC.
When software holds pincfg_mux and calls ptp_set_pinfunc, it will disable the function previous assigned and the current function of current pin calling ptp_disable_pinfunc.
The problem is the enable callback in ptp_disable_pinfunc may have to hold pincfg_mux for ptp_find_pin.

The calling should be like this,
ptp_set_pinfunc (hold pincfg_mux)
---> ptp_disable_pinfunc
   ---> .enable
      ---> ptp_find_pin (hold pincfg_mux)

Thanks.

quoted

+		 */
+		if (!on)
+			break;
+
+		pin = ptp_find_pin(ocelot->ptp_clock, PTP_PF_PEROUT,
+				   rq->perout.index);
+		if (pin == 0)
+			ptp_pin = PTP_PIN_0;
+		else if (pin == 1)
+			ptp_pin = PTP_PIN_1;
+		else if (pin == 2)
+			ptp_pin = PTP_PIN_2;
+		else if (pin == 3)
+			ptp_pin = PTP_PIN_3;
+		else
+			return -EINVAL;

Return -EBUSY here instead.

Thanks. Will modify it in next version.

Thanks,
Richard