linux-kernel - Re: [PATCH 7/7] net: dsa: b53: Expose PTP timestamping ioctls to userspace

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Date:   Sun, 7 Nov 2021 06:05:34 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Martin Kaistra <martin.kaistra@...utronix.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 7/7] net: dsa: b53: Expose PTP timestamping ioctls to
 userspace

On Sat, Nov 06, 2021 at 02:36:06AM +0200, Vladimir Oltean wrote:
> On Fri, Nov 05, 2021 at 05:18:04PM -0700, Richard Cochran wrote:
> > On Fri, Nov 05, 2021 at 04:28:33PM +0200, Vladimir Oltean wrote:
> > > What is the expected convention exactly? There are other drivers that
> > > downgrade the user application's request to what they support, and at
> > > least ptp4l does not error out, it just prints a warning.
> > 
> > Drivers may upgrade, but they may not downgrade.
> > 
> > Which drivers downgrade?  We need to fix those buggy drivers.
> > 
> > Thanks,
> > Richard
> 
> Just a quick example
> https://elixir.bootlin.com/linux/v5.15/source/drivers/net/ethernet/mscc/ocelot.c#L1178

        switch (cfg.rx_filter) {
        case HWTSTAMP_FILTER_NONE:
                break;
        case HWTSTAMP_FILTER_ALL:
        case HWTSTAMP_FILTER_SOME:
        case HWTSTAMP_FILTER_PTP_V1_L4_EVENT:
        case HWTSTAMP_FILTER_PTP_V1_L4_SYNC:
        case HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ:
        case HWTSTAMP_FILTER_NTP_ALL:
        case HWTSTAMP_FILTER_PTP_V2_L4_EVENT:
        case HWTSTAMP_FILTER_PTP_V2_L4_SYNC:
        case HWTSTAMP_FILTER_PTP_V2_L4_DELAY_REQ:
        case HWTSTAMP_FILTER_PTP_V2_L2_EVENT:
        case HWTSTAMP_FILTER_PTP_V2_L2_SYNC:
        case HWTSTAMP_FILTER_PTP_V2_L2_DELAY_REQ:
        case HWTSTAMP_FILTER_PTP_V2_EVENT:
        case HWTSTAMP_FILTER_PTP_V2_SYNC:
        case HWTSTAMP_FILTER_PTP_V2_DELAY_REQ:
                cfg.rx_filter = HWTSTAMP_FILTER_PTP_V2_EVENT;
                break;
        default:
                mutex_unlock(&ocelot->ptp_lock);
                return -ERANGE;
        }

That is essentially an upgrade to HWTSTAMP_FILTER_PTP_V2_EVENT.  The
change from ALL to HWTSTAMP_FILTER_PTP_V2_EVENT is probably a simple
oversight, and the driver can be easily fixed.

Thanks,
Richard