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

From: Peter Hilber <peter.hilber@opensynergy.com>
To: Andrew Lunn <andrew@lunn.ch>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
	linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
	virtio-dev@lists.oasis-open.org,
	linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org,
	"virtio-comment@lists.oasis-open.org"
	<virtio-comment@lists.oasis-open.org>,
	"Christopher S. Hall" <christopher.s.hall@intel.com>,
	Jason Wang <jasowang@redhat.com>,
	John Stultz <jstultz@google.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	netdev@vger.kernel.org,
	Richard Cochran <richardcochran@gmail.com>,
	Stephen Boyd <sboyd@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	Marc Zyngier <maz@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Alessandro Zummo <a.zummo@towertech.it>,
	"Ridoux, Julien" <ridouxj@amazon.com>
Subject: Re: [RFC PATCH v3 0/7] Add virtio_rtc module and related changes
Date: Thu, 14 Mar 2024 10:13:28 +0100	[thread overview]
Message-ID: <ed2769d7-1cbe-4e27-86b1-4ae365cceb28@opensynergy.com> (raw)
In-Reply-To: <04246331-e890-4c9a-95fb-9673580e6d30@lunn.ch>

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