linux-kernel - Re: [Xen-devel] [RFC/WIP] xen: clk: introudce pvclk for device passthrough

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Date:	Mon, 18 Jan 2016 11:22:44 +0000
From:	George Dunlap <George.Dunlap@...citrix.com>
To:	Peng Fan <van.freenix@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Julien Grall <julien.grall@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	linux-clk@...r.kernel.org
Subject: Re: [Xen-devel] [RFC/WIP] xen: clk: introudce pvclk for device passthrough

On Sat, Jan 16, 2016 at 5:22 AM, Peng Fan <van.freenix@...il.com> wrote:
> This patch was just a initial patch, not sure whether this way
> is ok from you side for handlding clk when doing platform device
> passhthrough. Any comments are appreciated, and your comments may
> give me a better direction.

Hey Peng,

Just speaking from the perspective of a Xen dev who's not an ARM dev:
a few more words on the relationship between pvclk and
device-passthrough would be helpful to set the context.  It sounds
like:

* On ARM, passing through a device requires a clocksource (at least
for many devices)

* dom0 has the hardware clocksource, but at the moment domUs don't
have a suitable clocksource

* This patch implements pvclk front/backend suitable for such devices

Is that right?  In which case something like the following would be helpful:

"This patch introduces pvclk, a paravirtualized clock source suitable
for devices to use when passing through to domUs on ARM systems."

(Obviously change it as necessary to make it accurate.)

Thanks,
 -George