linux-kernel - Re: [PATCH v3] clocksource: arch_timer: Allow the device tree to specify the physical timer

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Message-ID: <CAD=FV=WaNGeaXbYcHHBBYosX_0bpZVGCiqi=iuCXamcN3VEEpQ@mail.gmail.com>
Date:	Wed, 1 Oct 2014 08:21:49 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Sonny Rao <sonnyrao@...omium.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	"olof@...om.net" <olof@...om.net>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Christopher Covington <cov@...eaurora.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Nathan Lynch <Nathan_Lynch@...tor.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] clocksource: arch_timer: Allow the device tree to
 specify the physical timer

Hi,

On Mon, Sep 29, 2014 at 10:30 AM, Sonny Rao <sonnyrao@...omium.org> wrote:
> On Fri, Sep 26, 2014 at 3:00 AM, Mark Rutland <mark.rutland@....com> wrote:
>> On Thu, Sep 11, 2014 at 06:00:01PM +0100, Doug Anderson wrote:
>>> +** Optional properties:
>>> +
>>> +- arm,use-physical-timer : Don't ever use the virtual timer, just use the
>>> +  physical one.  Only supported for ARM (not ARM64).
>>
>> I'm still not keen on telling the kernel what to do rather than
>> describing the actual state of affairs and having the kernel decide what
>> to do. Perhaps what we actually need is:
>>
>> - cntvoff-not-fw-configured: Firmware does not configure CNTVOFF, which
>>   may reset to (different) arbitrary values on each CPU.
>>
>> This also doesn't describe that CNTHCTL.PL1PC(T)EN must both be 1. While
>> that is the reset state, it still feels dodbgy to me to rely on that.
>>
>> Mark.
>
> Mark, I'm happy to repost it with that name for Doug.
>
> I think it's fair to describe this state in the binding, and if a
> firmware were to put this property into the device-tree for and
> CNTHCTL.PL1P(T)CEN also have configured to 0, then the kernel can
> merely consider that to be a broken usage of this property.   We
> certainly can't protect against all of the possible invalid states
> caused and probably shouldn't try.  If we implement something like
> Christopher's suggestion for transitioning from secure svc to NS hyp
> mode then the kernel can simply ignore this property at that point.

I've already talked in person to Sonny about this, but just to post on
the list too...  I think Mark Rutland's suggestion is a good one and
I'm more than happy for Sonny to repost that way for me.  Thanks!  :)

-Doug
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