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

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Message-ID: <5217321B.6060306@arm.com>
Date:	Fri, 23 Aug 2013 10:57:47 +0100
From:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
	"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 23/08/13 10:26, Catalin Marinas wrote:
> 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.

Yes that seems reasonable. I assume we can enable it by default and we
need to disable it for hardware validation. Let me know if think otherwise.

Regards,
Sudeep

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