linux-kernel - Re: [PATCH] clocksource: arch_timer: Fix code to use physical timers when requested

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Date:	Wed, 27 Aug 2014 15:26:17 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Sonny Rao <sonnyrao@...omium.org>, Olof Johansson <olof@...om.net>
CC:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Russell King <linux@....linux.org.uk>,
	Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Doug Anderson <dianders@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <Mark.Rutland@....com>
Subject: Re: [PATCH] clocksource: arch_timer: Fix code to use physical timers
 when requested

+Mark (author of change in question)

On 08/27/14 14:27, Sonny Rao wrote:
> On Wed, Aug 27, 2014 at 2:19 PM, Olof Johansson <olof@...om.net> wrote:
>> On Wed, Aug 27, 2014 at 2:03 PM, Sonny Rao <sonnyrao@...omium.org> wrote:
>>> This is a bug fix for using physical arch timers when
>>> the arch_timer_use_virtual boolean is false.  It restores the
>>> arch_counter_get_cntpct() function after removal in
>>>
>>> 0d651e4e "clocksource: arch_timer: use virtual counters"
>>>
>>> and completes the implementation of memory mapped access for physical
>>> timers, so if a system is trying to use physical timers, it will
>>> function properly.
>>>
>>> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
>> Acked-by: Olof Johansson <olof@...om.net>
>>
>> This should have a:
>>
>> Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
>>
>> tag too, and possibly cc stable?
> Ok, as far as stable goes, this patch wouldn't apply cleanly going all
> the way back to  0d651e4e65e9
> As-is, it would need to go after 220069945b29 "clocksource:
> arch_timer: Add support for memory mapped timers" and there would need
> to be another, simpler, version that went between those two commits.
>
> So, I'm not sure what to do in this situation regarding stable?

Is there any reason why the virtual counter can't be read? Maybe we're
the hyp and we need to make sure we don't use the virtual timer so that
the guest can use it, but that doesn't have any effect on the usage of
the virtual counter for the clocksource.

-- 
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