linux-kernel - Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi

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Message-ID: <20151123213206.GG19156@codeaurora.org>
Date:	Mon, 23 Nov 2015 13:32:06 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Peter Maydell <peter.maydell@...aro.org>,
	Måns Rullgård <mans@...sr.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Christopher Covington <cov@...eaurora.org>
Subject: Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library
 functions

On 11/23, Arnd Bergmann wrote:
> On Monday 23 November 2015 12:38:47 Stephen Boyd wrote:
> > On 11/23, Arnd Bergmann wrote:
> > > On Monday 23 November 2015 09:14:39 Christopher Covington wrote:
> > > > On 11/23/2015 03:15 AM, Arnd Bergmann wrote:
> > > > LPAE is only supported in the Krait 450.
> > > > 
> > > > http://www.anandtech.com/show/7537/qualcomms-snapdragon-805-25ghz-128bit-memory-interface-d3d11class-graphics-more
> > > > 
> > > > I'm pretty sure idiv support came earlier, but I don't have the
> > > > specifics on hand.
> > > 
> > > I have seen that article, but didn't trust it as a canonical
> > > source of information here.
> > > 
> > > If you can confirm that it's right, that would mean that we
> > > don't support LPAE on mach-qcom, as the only SoC with Krait 450
> > > seems to be APQ8084, and mainline Linux doesn't run on that.
> > 
> > arch/arm/boot/dts/qcom-apq8084.dtsi exists in the mainline
> > kernel. We support more than what's in the Kconfig language
> > under mach-qcom.
> 
> Ok, cool. I'm sometimes confused by the model numbers, could you
> do a separate patch to update the Kconfig help text?

What did you have in mind? I'm also confused by the model numbers
so I don't know how helpful I will be.

It would be nice to drop the ARCH_MSM* configs entirely. If we
could select the right timers from kconfig without using selects
then we could drop them. Or we could just select both types of
timers when building qcom platforms.

> 
> > > The ones we do support are MSM8x60 (Scorpion), MSM8960
> > > (Krait-without-number),and MSM7874 (Krait 400). Do those all
> > > support IDIV but not LPAE?
> > > 
> > 
> > Krait supports IDIV for all versions. Scorpion doesn't support
> > IDIV or lpae. Here's the output of /proc/cpuinfo on that device. 
> > 
> > # cat /proc/cpuinfo
> > processor       : 0
> > model name      : ARMv7 Processor rev 2 (v7l)
> > BogoMIPS        : 13.50
> > Features        : half thumb fastmult vfp edsp neon vfpv3 tls vfpd32
> > CPU implementer : 0x51
> > CPU architecture: 7
> > CPU variant     : 0x0
> > CPU part        : 0x02d
> > CPU revision    : 2
> 
> Ok, that leaves just one missing puzzle piece: can you confirm that
> no supported Krait variant other than Krait 450 / apq8084 has LPAE?
> 

Right, apq8084 is the only SoC with a Krait CPU that supports
LPAE.

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