Re: [RFC V2] xen: interface: introduce pvclk interface

From: "Jan Beulich" <JBeulich@suse.com>
To: Peng Fan <van.freenix@gmail.com>
Cc: Ian Campbell <ian.campbell@citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Julien Grall <julien.grall@citrix.com>,
	David Vrabel <david.vrabel@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [RFC V2] xen: interface: introduce pvclk interface
Date: Thu, 21 Jan 2016 03:21:38 -0700	[thread overview]
Message-ID: <56A0BF4202000078000C980B@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160121085858.GA15664@linux-7smt.suse>

>>> On 21.01.16 at 09:59, <van.freenix@gmail.com> wrote:
> uart2 needs clock IMX7D_UART2_ROOT_CLK from the ccm.
> passthrough uart2, hypervisor handles the reg and interrupts, that is 
> because
> hypervisor handles the memory map and the interrupt controller(GIC). But 
> here
> CCM is not handled by hypervisor, it is handled by Dom0.

This, I take it, describes the current state, which doesn't make clear
whether this is intentionally that way (and can't be changed), or
just happens to be that way because so far it didn't matter.

> For ARMV8 server products, I am not sure whether hypercall is better; but to 
> my case, it's not feasible to use hypercall.

Because of ...?

> Dom0 handles all the clocks, DomU just send request to Dom0 and ask Dom0 to
> enable/disable/set rate for a clock for the device. So I think it's okay
> for multipile parties, the clk subsystem in Dom0 can handle mutiple requests 
> even if the clock is shared.

I.e. if one party sets one rate, and later another party sets
a different rate, things are going to work fine? If so, why would
the different parties need control over the rate in the first place?

Jan