linux-kernel - Re: [PATCH v6 4/5] drivers: clocksource: add support for ARM architected timer event stream

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Message-ID: <521F6BDF.2050909@arm.com>
Date:	Thu, 29 Aug 2013 16:42:23 +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 v6 4/5] drivers: clocksource: add support for ARM architected
 timer event stream

On 29/08/13 16:39, Catalin Marinas wrote:
> On Thu, Aug 29, 2013 at 03:55:41PM +0100, Sudeep KarkadaNagesha wrote:
>> From: Will Deacon <will.deacon@....com>
>>
>> The ARM architected timer can generate events (used for waking up
>> CPUs executing the wfe instruction) at a frequency represented as a
>> power-of-2 divisor of the clock rate.
>>
>> An event stream might be used:
>> - To impose a time-out on a wfe polling loop.
>> - To safeguard against any programming error in case an expected event
>>   is not generated.
>> - To implement wfe-based timeouts for userspace locking implementations.
>>
>> This patch computes the event stream frequency aiming for a period
>> of 100us between events. It uses ARM/ARM64 specific backends to configure
>> and enable the event stream.
>>
>> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Signed-off-by: Will Deacon <will.deacon@....com>
>> [sudeep: moving ARM/ARM64 changes into separate patches
>>          and adding Kconfig option]
>> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
>> ---
>>  drivers/clocksource/Kconfig          | 14 ++++++++++++++
>>  drivers/clocksource/arm_arch_timer.c | 15 +++++++++++++++
>>  include/clocksource/arm_arch_timer.h |  2 ++
>>  3 files changed, 31 insertions(+)
>>
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index b7b9b04..49f1f6e 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -74,6 +74,20 @@ config ARM_ARCH_TIMER
>>  	bool
>>  	select CLKSRC_OF if OF
>>  
>> +config ARM_ARCH_TIMER_EVTSTREAM
>> +	bool "Support for ARM architected timer event stream generation"
>> +	default y if ARM_ARCH_TIMER
>> +	help
>> +	  This option enables support for event stream generation based on
>> +	  the ARM architected timer. It is used for waking up CPUs executing
>> +	  the wfe instruction at a frequency represented as a power-of-2
>> +	  divisor of the clock rate. An event stream might be mainly useful
>> +	  for wfe-based timeouts for userspace locking implementations.
> 
> I would be a bit more assertive here, something like "the main use of
> the event stream is wfe-based timeouts of userspace locking
> implementations."
> 
>> +	  It might also be useful for imposing timeout on a wfe or even
>> +	  safeguarding against any programming errors in case an expected
> 
> Maybe "imposting timeout on wfe to safeguard against ...". We already
> mentioned wfe-based timeout above.
> 
Ok will fix this Kconfig description.

> Otherwise, for the whole series:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> 
Thanks.

Regards,
Sudeep

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