netdev - Re: [PATCH net-next 8/8] net: mscc: PTP Hardware Clock (PHC) support

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Message-ID: <20190705215843.ncku546l3lktpwni@localhost>
Date:   Fri, 5 Jul 2019 14:58:43 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     davem@...emloft.net, alexandre.belloni@...tlin.com,
        UNGLinuxDriver@...rochip.com, ralf@...ux-mips.org,
        paul.burton@...s.com, jhogan@...nel.org, netdev@...r.kernel.org,
        linux-mips@...r.kernel.org, thomas.petazzoni@...tlin.com,
        allan.nielsen@...rochip.com
Subject: Re: [PATCH net-next 8/8] net: mscc: PTP Hardware Clock (PHC) support

On Mon, Jul 01, 2019 at 12:03:27PM +0200, Antoine Tenart wrote:

> +static irqreturn_t ocelot_ptp_rdy_irq_handler(int irq, void *arg)
> +{
> +	struct ocelot *ocelot = arg;
> +
> +	do {
> +		struct skb_shared_hwtstamps shhwtstamps;
> +		struct list_head *pos, *tmp;
> +		struct ocelot_skb *entry;
> +		struct ocelot_port *port;
> +		struct timespec64 ts;
> +		struct sk_buff *skb = NULL;
> +		u32 val, id, txport;
> +
> +		val = ocelot_read(ocelot, SYS_PTP_STATUS);
> +
> +		/* Check if a timestamp can be retrieved */
> +		if (!(val & SYS_PTP_STATUS_PTP_MESS_VLD))
> +			break;

Instead of an infinite do/while loop, I suggest a for loop bounded by
number of iterations or by execution time.  That would avoid getting
stuck here forever.  After all, this code is an ISR.

Thanks,
Richard

> +		WARN_ON(val & SYS_PTP_STATUS_PTP_OVFL);
> +
> +		/* Retrieve the ts ID and Tx port */
> +		id = SYS_PTP_STATUS_PTP_MESS_ID_X(val);
> +		txport = SYS_PTP_STATUS_PTP_MESS_TXPORT_X(val);
> +
> +		/* Retrieve its associated skb */
> +		port = ocelot->ports[txport];
> +
> +		list_for_each_safe(pos, tmp, &port->skbs) {
> +			entry = list_entry(pos, struct ocelot_skb, head);
> +			if (entry->id != id)
> +				continue;
> +
> +			skb = entry->skb;
> +
> +			list_del(pos);
> +			kfree(entry);
> +		}
> +
> +		/* Next ts */
> +		ocelot_write(ocelot, SYS_PTP_NXT_PTP_NXT, SYS_PTP_NXT);
> +
> +		if (unlikely(!skb))
> +			continue;
> +
> +		/* Get the h/w timestamp */
> +		ocelot_get_hwtimestamp(ocelot, &ts);
> +
> +		/* Set the timestamp into the skb */
> +		memset(&shhwtstamps, 0, sizeof(shhwtstamps));
> +		shhwtstamps.hwtstamp = ktime_set(ts.tv_sec, ts.tv_nsec);
> +		skb_tstamp_tx(skb, &shhwtstamps);
> +
> +		dev_kfree_skb_any(skb);
> +	} while (true);
> +
> +	return IRQ_HANDLED;
> +}