linux-kernel - Re: [PATCH] arm64: Disallow combination of ARCH

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Message-ID: <20160128112033.GI17123@leverpostej>
Date:	Thu, 28 Jan 2016 11:20:33 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Will Deacon <will.deacon@....com>, ard.biesheuvel@...aro.org,
	jeremy.linton@....com
Cc:	Catalin Marinas <catalin.marinas@....com>, Feng Kan <fkan@....com>,
	dann frazier <dann.frazier@...onical.com>,
	Duc Dang <dhdang@....com>, linux-kernel@...r.kernel.org,
	Loc Ho <lho@....com>, Kumar Sankaran <ksankaran@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: Disallow combination of ARCH_XGENE and 16K page
 size

On Thu, Jan 28, 2016 at 11:08:20AM +0000, Will Deacon wrote:
> On Thu, Jan 28, 2016 at 10:34:41AM +0000, Catalin Marinas wrote:
> > On Wed, Jan 27, 2016 at 04:10:30PM -0700, dann frazier wrote:
> > > 16K page size is an optional feature of the architecture, and is not
> > > supported by the X-Gene SoC family.
> > > 
> > > Signed-off-by: dann frazier <dann.frazier@...onical.com>
> > > ---
> > >  arch/arm64/Kconfig.platforms | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/arch/arm64/Kconfig.platforms b/arch/arm64/Kconfig.platforms
> > > index 21074f6..b241290 100644
> > > --- a/arch/arm64/Kconfig.platforms
> > > +++ b/arch/arm64/Kconfig.platforms
> > > @@ -133,6 +133,7 @@ config ARCH_VEXPRESS
> > >  
> > >  config ARCH_XGENE
> > >  	bool "AppliedMicro X-Gene SOC Family"
> > > +	depends on !ARM64_16K_PAGES
> > >  	help
> > >  	  This enables support for AppliedMicro X-Gene SOC Family
> > 
> > This would be the case on Juno as well. But maybe at some point the
> > X-Gene family would gain a CPU with such support.
> > 
> > Anyway, I would rather make 16K pages depend on EXPERT, make it a bit
> > harder to enable. We've had a few questions recently about enabling it
> > on CPUs that don't have such feature.
> 
> I thought there was also a suggestion that we could fail gracefully in
> the EFI stub if we detected an unsupported page size?

Yup. There are other things we could/should test, too.

I believe Jeremy had a patch, but due to churn in that area it didn't
get picked up.

Mark.