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

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Date:	Thu, 28 Aug 2014 13:09:32 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	Mark Rutland <mark.rutland@....com>
CC:	Doug Anderson <dianders@...omium.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sonny Rao <sonnyrao@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clocksource: arch_timer: Fix code to use physical timers
 when requested

Hi Mark,

On 08/28/2014 05:35 AM, Mark Rutland wrote:
> On Thu, Aug 28, 2014 at 04:33:31AM +0100, Doug Anderson wrote:
>> Hi,
>>
>> On Wed, Aug 27, 2014 at 7:58 PM, Olof Johansson <olof@...om.net> wrote:
>>> On Wed, Aug 27, 2014 at 5:56 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>>>> On 08/27/14 15:33, Olof Johansson wrote:
>>>>> On Wed, Aug 27, 2014 at 3:26 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>>>>>
>>>>>> 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.
>>>>>
>>>>> There are several cases where virtual is unusable -- in particular it
>>>>> might not have been configured properly (i.e. the phys/virt offset is
>>>>> at a bad value).
>>>>
>>>> Any specifics? It would be nice to say so in the commit text so that
>>>> others using such devices know they need this patch. I'm guessing the
>>>> firmware can't be fixed?
>>
>> Even if we could change things to use a virtual timer in some cases,
>> Sonny's patch still fixes a bug.  The code as written right now makes
>> pretenses about supporting the physical timer, but it doesn't work.
>> That should be fixed.
> 
> The code does support the physical timer. It does not support the
> physical counter (and makes no pretenses that it does).

I think if you could please explain the following code, that may help clear up
some of the confusion.

		if (arch_timer_use_virtual) {
			clk->irq = arch_timer_ppi[VIRT_PPI];
			clk->set_mode = arch_timer_set_mode_virt;
			clk->set_next_event = arch_timer_set_next_event_virt;
		} else {
			clk->irq = arch_timer_ppi[PHYS_SECURE_PPI];
			clk->set_mode = arch_timer_set_mode_phys;
			clk->set_next_event = arch_timer_set_next_event_phys;
		}

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/clocksource/arm_arch_timer.c#n272

Perhaps you mean to say the code does not support *non-secure access* to the
physical timer?

Thanks,
Christopher

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