netdev - Re: [RFC PATCH v3 0/7] Add virtio_rtc module and related changes

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Date: Thu, 14 Mar 2024 10:13:28 +0100
From: Peter Hilber <peter.hilber@...nsynergy.com>
To: Andrew Lunn <andrew@...n.ch>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: David Woodhouse <dwmw2@...radead.org>, linux-kernel@...r.kernel.org,
 virtualization@...ts.linux.dev, virtio-dev@...ts.oasis-open.org,
 linux-arm-kernel@...ts.infradead.org, linux-rtc@...r.kernel.org,
 "virtio-comment@...ts.oasis-open.org" <virtio-comment@...ts.oasis-open.org>,
 "Christopher S. Hall" <christopher.s.hall@...el.com>,
 Jason Wang <jasowang@...hat.com>, John Stultz <jstultz@...gle.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
 Richard Cochran <richardcochran@...il.com>, Stephen Boyd <sboyd@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Xuan Zhuo
 <xuanzhuo@...ux.alibaba.com>, Marc Zyngier <maz@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Alessandro Zummo <a.zummo@...ertech.it>, "Ridoux, Julien"
 <ridouxj@...zon.com>
Subject: Re: [RFC PATCH v3 0/7] Add virtio_rtc module and related changes

On 13.03.24 21:12, Andrew Lunn wrote:
>> As long as it doesn't behave differently from the other RTC, I'm fine
>> with this. This is important because I don't want to carry any special
>> infrastructure for this driver or to have to special case this driver
>> later on because it is incompatible with some evolution of the
>> subsystem.
> 
> Maybe deliberately throw away all the sub-second accuracy when
> accessing the time via the RTC API? That helps to make it look like an
> RTC. And when doing the rounding, add a constant offset of 10ms to
> emulate the virtual i2c bus it is hanging off, like most RTCs?
> 
> 	  Andrew

The truncating to whole seconds is already done. As to the offset, I do not
understand how this would help. I can read out my CMOS RTC in ~50 us.

Thanks for the comment,

Peter