Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

From: Stephen Boyd
Date: Mon Nov 23 2015 - 15:38:55 EST

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:
> > > On Sunday 22 November 2015 21:36:45 Nicolas Pitre wrote:
> > >> On Sun, 22 Nov 2015, Arnd Bergmann wrote:
> > >
> > > Ok, thanks a lot! So the reporting in /proc/cpuinfo clearly matches
> > > the actual features, and we can just treat this as no LPAE / no IDIV
> > > for kernel compilation, as nobody ever seems to use THUMB2_KERNEL
> > > in practice.
> > >
> > > PJ4-MP is like Cortex-A15/A7/A12/A17 and supports both IDIV and LPAE,
> > > which leaves the question whether Scorpion or Krait do the same as
> > > well, or whether they are outliers and need a special configuration.
> >
> > 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. 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
CPU implementer : 0x51
CPU architecture: 7
CPU variant : 0x3
CPU part : 0x06f
CPU revision : 1

processor : 1
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
CPU implementer : 0x51
CPU architecture: 7
CPU variant : 0x3
CPU part : 0x06f
CPU revision : 1

processor : 2
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
CPU implementer : 0x51
CPU architecture: 7
CPU variant : 0x3
CPU part : 0x06f
CPU revision : 1

processor : 3
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
CPU implementer : 0x51
CPU architecture: 7
CPU variant : 0x3
CPU part : 0x06f
CPU revision : 1

Hardware : Qualcomm (Flattened Device Tree)
Revision : 0000
Serial : 0000000000000000

>
> 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

processor : 1
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

Hardware : Qualcomm (Flattened Device Tree)
Revision : 0000
Serial : 0000000000000000

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