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

From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Peter Hilber <peter.hilber@opensynergy.com>,
	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: Wed, 13 Mar 2024 15:50:54 +0100	[thread overview]
Message-ID: <202403131450547f373268@mail.local> (raw)
In-Reply-To: <96be7312f7bddaf06c690e082a8028fa8b511deb.camel@infradead.org>

On 13/03/2024 14:06:42+0000, David Woodhouse wrote:
> If you're asking why patch 7/7 in Peter's series exists to expose the
> virtio clock through RTC, and you're not particularly interested in the
> first six, I suppose that's a fair question. As is the question of "why
> is it called virtio_rtc not virtio_ptp?". 
> 

Exactly my question, thanks :)

> But let me turn it around: if the kernel has access to this virtio
> device and *not* any other RTC, why *wouldn't* the kernel use the time
> from it? The fact that it can optionally *also* provide paired readings
> with the CPU counter doesn't actually *hurt* for the RTC use case, does
> it?

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.

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com