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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id c7sm781106qtw.70.2020.12.02.18.04.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Dec 2020 18:04:28 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kkdyt-005ISu-Nz; Wed, 02 Dec 2020 22:04:27 -0400 Date: Wed, 2 Dec 2020 22:04:27 -0400 From: Jason Gunthorpe To: Thomas Gleixner Cc: Miroslav Lichvar , linux-kernel@vger.kernel.org, John Stultz , Prarit Bhargava , Alessandro Zummo , Alexandre Belloni , linux-rtc@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH] rtc: adapt allowed RTC update error Message-ID: <20201203020427.GR5487@ziepe.ca> References: <20201201143835.2054508-1-mlichvar@redhat.com> <20201201161224.GF5487@ziepe.ca> <20201201171420.GN1900232@localhost> <20201201173540.GH5487@ziepe.ca> <87mtywe2zu.fsf@nanos.tec.linutronix.de> <20201202162723.GJ5487@ziepe.ca> <87a6uwdnfn.fsf@nanos.tec.linutronix.de> <20201202205418.GN5487@ziepe.ca> <874kl3eu8p.fsf@nanos.tec.linutronix.de> <87zh2vd72z.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87zh2vd72z.fsf@nanos.tec.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 03, 2020 at 02:14:12AM +0100, Thomas Gleixner wrote: > If anyone involved seriously believes that any of this solves a real > world problem, then please come forth an make your case. The original commit 0f295b0650c9 ("rtc: Allow rtc drivers to specify the tv_nsec value for ntp") was tested by myself and RMK on various ARM systems and did work as advertised. Here is the giant thread, RMK's post explains the problem and gives his measurements of several different RTCs: https://lore.kernel.org/linux-arm-kernel/20170920112152.GL20805@n2100.armlinux.org.uk/ And the patch that resulted: https://lore.kernel.org/linux-arm-kernel/20171013175433.GA22062@obsidianresearch.com/ There is a lot of detail in there.. Keep in mind none of this was for the mc146818 style RTCs. I can't recall any more why no drivers use the set_offset_nsec. I'm surprised, maybe I forgot to send the patch for the RTCs I tested or maybe it got dropped someplace.. It certainly was needed for some maxim I2C chips. The thread shows rmk had even written a hrtimer patch to go with this, but it also got lost for some reason. Maybe all the arguing killed further effort? Jason