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SubjectRE: [PATCH 6/6] ptp_ocelot: support 4 programmable pins
Date
> -----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
> <davem@davemloft.net>; Vladimir Oltean <vladimir.oltean@nxp.com>;
> Claudiu Manoil <claudiu.manoil@nxp.com>; Andrew Lunn <andrew@lunn.ch>;
> Vivien Didelot <vivien.didelot@gmail.com>; Florian Fainelli
> <f.fainelli@gmail.com>; Alexandre Belloni <alexandre.belloni@bootlin.com>;
> Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
> Subject: Re: [PATCH 6/6] ptp_ocelot: support 4 programmable pins
>
> On Fri, Mar 20, 2020 at 06:37:26PM +0800, Yangbo Lu wrote:
> > +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.

>
> > + */
> > + 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

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