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From: Sudeep Holla <sudeep.holla@arm.com>
To: Jon Mason <jon.mason@broadcom.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>,
	Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC 1/1] ARM: print MHz in /proc/cpuinfo
Date: Thu, 9 Jun 2016 10:09:25 +0100	[thread overview]
Message-ID: <57593245.5020109@arm.com> (raw)
In-Reply-To: <20160608193003.GA17688@broadcom.com>



On 08/06/16 20:31, Jon Mason wrote:
> On Wed, Jun 08, 2016 at 09:34:06AM +0100, Sudeep Holla wrote:
>>
>>
>> On 07/06/16 22:08, Jon Mason wrote:
>>> Query the CPU core clock in the device tree to determine the core clock
>>> speed.
>>
>> How do guarantee that it's the current frequency of the CPU ?
>
> I am basing it on the assumption (perhaps incorrect) that the clock in
> the CPU DT corresponds to the one determining the CPU clock rate.  And,
> that this clock rate is accurate in describing the speed at which the
> CPU is currently running.
>

As you already noticed, it's not always correct.

[..]

>>
>> What if they just don't have in DT but have DVFS support ?
>
> This can be extended to cover DVFS or SMC calls or anything else.
> This was simply a first step to cover what appeared to be the most
> prevalent case.
>

Using DVFS/CPUFreq makes this DT based approach irrelevant.

>> Also whey do we need this support when the user-space can query the
>> CPUFreq sysfs which is more accurate and maintains the current running
>> frequency ?
>
> This is exactly what x86 is doing to provide its value in
> /proc/cpuinfo.  I could easily augment this patch to call
> cpufreq_quick_get(), if it returns 0, then call clk_get_rate().  If
> both return 0, then simply not print out anything (which would cover
> all of the possibilities).  Or, I could have it just call
> cpufreq_quick_get() to get the value.
>

Agree x86 has, may be for legacy reasons. It even has CPUFreq sysfs
entries which is architecture agnostic while /proc/cpuinfo is more
architecture based. So applications that want to be portable across
architectures must choose the generic CPUFreq sysfs path rather than
some x86 based cpuinfo.

-- 
Regards,
Sudeep

  reply	other threads:[~2016-06-09  9:09 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-07 21:08 [RFC 0/1] " Jon Mason
2016-06-07 21:08 ` [RFC 1/1] " Jon Mason
2016-06-08  8:34   ` Sudeep Holla
2016-06-08 19:31     ` Jon Mason
2016-06-09  9:09       ` Sudeep Holla [this message]
2016-06-09 17:36         ` Jon Mason
2016-06-07 22:18 ` [RFC 0/1] " Russell King - ARM Linux
2016-06-07 22:58   ` Jon Mason
2016-07-02 23:58   ` Jon Masters
2016-07-03 16:54     ` Russell King - ARM Linux
2016-07-03 18:49       ` Andrew Lunn
2016-07-03 19:10         ` Russell King - ARM Linux
2016-07-18 10:02       ` Pavel Machek

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