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

From: Richard Cochran <[email-masked]>
Date: Wed, 24 Jun 2020 06:03:18 -0700

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

> diff --git a/drivers/net/dsa/hirschmann/hellcreek.h b/drivers/net/dsa/hirschmann/hellcreek.h
> index a08a10cb5ab7..2d4422fd2567 100644
> --- a/drivers/net/dsa/hirschmann/hellcreek.h
> +++ b/drivers/net/dsa/hirschmann/hellcreek.h
> @@ -234,10 +234,17 @@ struct hellcreek_fdb_entry {
>  struct hellcreek {
>  	struct device *dev;
>  	struct dsa_switch *ds;
> +	struct ptp_clock *ptp_clock;
> +	struct ptp_clock_info ptp_clock_info;
>  	struct hellcreek_port ports[4];
> +	struct delayed_work overflow_work;
>  	spinlock_t reg_lock;	/* Switch IP register lock */
> +	spinlock_t ptp_lock;	/* PTP IP register lock */

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