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

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Date:	Mon, 23 Nov 2015 22:19:21 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Stephen Boyd <sboyd@...eaurora.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 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?

> And yes LPAE is supported by apq8084 (as is
> IDIV). Here's the /proc/cpuinfo on that device.
> # cat /proc/cpuinfo
> processor       : 0
> model name      : ARMv7 Processor rev 1 (v7l)
> BogoMIPS        : 38.40
> Features        : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm

Ok.

> > 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?

	Arnd 
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