linux-kernel - Re: [PATCH] powercap / RAPL : remove dependency on iosf

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Message-ID: <20150922085730.14bafdec@icelake>
Date:	Tue, 22 Sep 2015 08:57:30 -0700
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Austin S Hemmelgarn <ahferroin7@...il.com>
Cc:	Pengyu Ma <pengyu.ma@...driver.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	rafael.j.wysocki@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powercap / RAPL : remove dependency on iosf_mbi

On Tue, 22 Sep 2015 09:41:52 -0400
Austin S Hemmelgarn <ahferroin7@...il.com> wrote:

> On 2015-09-21 17:36, Jacob Pan wrote:
> > On Mon, 21 Sep 2015 11:48:14 +0800
> > Pengyu Ma <pengyu.ma@...driver.com> wrote:
> >
> >>
> >>
> >> On 09/18/2015 11:43 PM, Jacob Pan wrote:
> >>> On Fri, 18 Sep 2015 02:09:55 +0200
> >>> "Rafael J. Wysocki" <rjw@...ysocki.net> wrote:
> >>>
> >>>> On Thursday, September 17, 2015 03:31:41 PM Pengyu Ma wrote:
> >>>>> iosf_mbi is supported on Quark, Braswell, Baytrail and some Atom
> >>>>> SoC, but RAPL is not limited to these SoC, it supports almost
> >>>>> Intel CPUs. Remove this dependece to make RAPL support more
> >>>>> Intel CPUs.
> >>>>>
> >>>>> Please select IOSF_MBI on Atom SoCs.
> >>>>>
> >>> Unlike Quark, I don't think we want to or do differentiate Atom
> >>> from other x86 at compile time. IOSF driver can be compiled as a
> >>> module also, therefore RAPL driver needs this explicit dependency
> >>> at compile time.
> >> As commit had exported iosf_mbi to let user use it.
> >>
> >> commit aa8e4f22ab7773352ba3895597189b8097f2c307
> >> Author: David E. Box <david.e.box@...ux.intel.com>
> >> Date:   Wed Aug 27 14:40:39 2014 -0700
> >>
> >>       x86/iosf: Add Kconfig prompt for IOSF_MBI selection
> >>
> >>
> >> While selecting IOSF_MBI is preferred, it does mean carrying extra
> >> code on non-SoC architectures.
> >>
> >> We can NOT force user to build in iosf_mbi if they want use RAPL on
> >> haswell/broadwell/skylake.
> >> And RAPL can be compiled and worked well on
> >> haswell/broadwell/skylake without IOSF_MBI.
> >> RAPL is really NOT depended on IOSF_MBI.
> >>
> > True for haswell/broadwell/skylake platforms. But if we want binary
> > compatibility for Atom and Core, I can' see how simply removing the
> > dependency would work, unless we have runtime detection of IOSF.
> So make RAPL select IOSF instead of depending on it, add something to 
> the RAPL help text saying that IOSF is needed for it to work on
> SoC's, and make IOSF=y in the defconfig.
> 
> This way, people who just turn on RAPL support should get IOSF,
> whereas people like me who actually build custom kernels for each
> system we own aren't forced to include yet more code that is 100%
> useless for us.
> 
If you build a custom kernel for Core with RAPL, your kernel would still
"select" IOSF which is not needed. right?

> It's also worth noting that most of the people who care about binary 
> compatibility for a wide variety of chips in one kernel (read as
> 'distro maintainers') will be turning IOSF on anyway, because it's
> needed for other things on chips that have it to work right as well.
> >
true. no issue for that case.
> >> Pengyu
> >>>>> Signed-off-by: Pengyu Ma <pengyu.ma@...driver.com>
> >>>> Jacob?
> >>>>
> >>>>> ---
> >>>>>    drivers/powercap/Kconfig | 2 +-
> >>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/powercap/Kconfig b/drivers/powercap/Kconfig
> >>>>> index 85727ef..a7c81b5 100644
> >>>>> --- a/drivers/powercap/Kconfig
> >>>>> +++ b/drivers/powercap/Kconfig
> >>>>> @@ -17,7 +17,7 @@ if POWERCAP
> >>>>>    # Client driver configurations go here.
> >>>>>    config INTEL_RAPL
> >>>>>    	tristate "Intel RAPL Support"
> >>>>> -	depends on X86 && IOSF_MBI
> >>>>> +	depends on X86
> >>>>>    	default n
> >>>>>    	---help---
> >>>>>    	  This enables support for the Intel Running Average
> >>>>> Power Limit (RAPL)
> >>>>>
> >>> [Jacob Pan]
> >>
> >
> > [Jacob Pan]
> > --
> > To unsubscribe from this list: send the line "unsubscribe
> > linux-kernel" in the body of a message to majordomo@...r.kernel.org
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> > Please read the FAQ at  http://www.tux.org/lkml/
> >
> 
> 

[Jacob Pan]
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