linux-kernel - Re: [PATCH v3 0/6] ARM/ARM64 architected timer updates

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Message-ID: <20130823092610.GB20186@darko.cambridge.arm.com>
Date:	Fri, 23 Aug 2013 10:26:10 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Will Deacon <Will.Deacon@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v3 0/6] ARM/ARM64 architected timer updates

On Tue, Aug 20, 2013 at 06:14:52PM +0100, Sudeep KarkadaNagesha wrote:
> On 13/08/13 18:29, Sudeep KarkadaNagesha wrote:
> > From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
> > 
> > This patch series adds support to configure the rate and enable the
> > event stream for architected timer. The event streams can be used to
> > impose a timeout on a WFE, to safeguard against any programming error
> > in case an expected event is not generated or even to implement
> > wfe-based timeouts for userspace locking implementations.
> > 
> > Since the timer control register is reset to zero on warm boot, CPU
> > PM notifier is added to re-initialize it.
> > 
> > Changes v2->v3:
> > 1. Moved ARM and ARM64 changes into separate patches
> > 2. Added native hwcaps definations(ARM/ARM64) and compat-specific
> >    definitions(ARM64) to the users for the event stream feature. 
> 
> Can you review this version of the series ?

I think the series is OK with the follow-up comments addressed. Could
you please post a v4 to make sure I haven't missed anything?

Another comment I have is whether we should make this feature
configurable. The reason is mainly hardware validation: if some CPU
implementation messes the event generation (and on ARMv8 it's a bit more
complex as this is tied to the exclusive monitor) we risk not detecting
it because of the event stream.

Thanks.

-- 
Catalin
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