linux-kernel - Re: [PATCH net-next v2 09/11] net: dsa: microchip: ksz9477: add hardware time stamping support

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Message-ID: <20201113033139.GC32138@hoboy.vegasvil.org>
Date:   Thu, 12 Nov 2020 19:31:39 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Christian Eggers <ceggers@...i.de>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Kurt Kanzenbach <kurt.kanzenbach@...utronix.de>,
        George McCollister <george.mccollister@...il.com>,
        Marek Vasut <marex@...x.de>,
        Helmut Grohne <helmut.grohne@...enta.de>,
        Paul Barker <pbarker@...sulko.com>,
        Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>,
        Tristram Ha <Tristram.Ha@...rochip.com>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 09/11] net: dsa: microchip: ksz9477: add
 hardware time stamping support

On Fri, Nov 13, 2020 at 04:40:20AM +0200, Vladimir Oltean wrote:
> > @@ -103,6 +108,10 @@ static int ksz9477_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
> >  	if (ret)
> >  		goto error_return;
> >
> > +	spin_lock_irqsave(&dev->ptp_clock_lock, flags);
> 
> I believe that spin_lock_irqsave is unnecessary, since there is no code
> that runs in hardirq context.

The .adjtime method is in a system call context.  If all of the code
that manipulates dev->ptp_clock_time can sleep, then you can use a
mutex.  Otherwise spin_lock_irqsave is the safe choice.

Thanks,
Richard