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Miller" , Sekhar Nori , Richard Cochran , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] net: cpts: Condition WARN_ON on PTP_1588_CLOCK Message-ID: <20200420093610.GA28162@arctic-shiba-lx> References: <20200416085627.1882-1-clay@daemons.net> <6fef3a00-6c18-b775-d1b4-dfd692261bd3@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6fef3a00-6c18-b775-d1b4-dfd692261bd3@ti.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 16, 2020 at 02:11:45PM +0300, Grygorii Strashko wrote: Grygorii, > > CPTS_MOD merely implies PTP_1588_CLOCK; it is possible to build cpts > > without PTP clock support. In that case, ptp_clock_register() returns > > NULL and we should not WARN_ON(cpts->clock) when downing the interface. > > The ptp_*() functions are stubbed without PTP_1588_CLOCK, so it's safe > > to pass them a null pointer. > > Could you explain the purpose of the exercise (Enabling CPTS with > PTP_1588_CLOCK disabled), pls? Hardware timestamping with a free-running PHC _almost_ works without PTP_1588_CLOCK, but since PHC rollover is handled by the PTP kworker in this driver the timestamps end up not being monotonic. And of course the moment you want to syntonize/synchronize the PHC with another clock (say, CLOCK_REALTIME), you'll need a PTP clock device. So you're right, there's not much point in building CPTS_MOD without PTP_1588_CLOCK. Given that, I wonder why all the Ethernet drivers seem to just `imply` PTP_1588_CLOCK, rather than `depends on` it? In any case, I was surprised to get a warning during `ifdown` but not during `ifup`. What do you think of this change, which prints an error like this during `ifup` if PTP_1588_CLOCK is not enabled: [ 6.192707] 000: cpsw 4a100000.ethernet: error registering cpts device --- diff --git a/drivers/net/ethernet/ti/cpts.c b/drivers/net/ethernet/ti/cpts.c index 10ad706dda53..70b15039cd37 100644 --- a/drivers/net/ethernet/ti/cpts.c +++ b/drivers/net/ethernet/ti/cpts.c @@ -462,8 +462,8 @@ int cpts_register(struct cpts *cpts) timecounter_init(&cpts->tc, &cpts->cc, ktime_get_real_ns()); cpts->clock = ptp_clock_register(&cpts->info, cpts->dev); - if (IS_ERR(cpts->clock)) { - err = PTR_ERR(cpts->clock); + if (IS_ERR_OR_NULL(cpts->clock)) { + err = cpts->clock ? PTR_ERR(cpts->clock) : -EOPNOTSUPP; cpts->clock = NULL; goto err_ptp; } --  Clay