| Message ID | 5651094A.5080607@mind.be |
|---|---|
| State | Not Applicable |
| Headers | show |
On 11/22/15 01:16, Arnout Vandecappelle wrote: Thanks for your follow up! > You have a good point. I don't think it's possible to have a NEON core without > VFP floating point unit. Hm, looking at [1], NEON and FPU are independently > optional, so theoretically you could have a Cortex-A9 with one but not the > other. But that probably doesn't exist in practice (in fact, we don't know any > Cortex-A9 that doesn't have both). You are right, I dived further into it: http://www.arm.com/cortex-a9.php Advanced SIMD NEON™ unit (Optional) and Cortex-A9 Floating-Point Unit (FPU) (Optional) But... as you also state, I have never seen any Cortex-A8 or higher witout a VFP-unit. Anyone? Because that's stupid of me, but I advise clients about (TI though) Cortex-A8 and higher in always having a VFP unit... > However, I think it should be fixed in Config.in.arm instead. Basically, > whenever NEON is selected, the VFP's 'maybe' should be converted into a 'has'. > So something like > > --- a/arch/Config.in.arm > +++ b/arch/Config.in.arm > @@ -244,6 +244,9 @@ config BR2_ARM_ENABLE_NEON > bool "Enable NEON SIMD extension support" > depends on BR2_ARM_CPU_MAYBE_HAS_NEON > select BR2_ARM_CPU_HAS_NEON > + select BR2_ARM_CPU_HAS_VFPV3 if BR2_ARM_CPU_MAYBE_HAS_VFPV3 > + select BR2_ARM_CPU_HAS_VFPV4 if BR2_ARM_CPU_MAYBE_HAS_VFPV4 > help > For some CPU cores, the NEON SIMD extension is optional. > Select this option if you are certain your particular > > (Note that the VFPv2 cores never have NEON - at least as far as I know. Checked > arm.com and that seems to be correct.) Agree. I see the compiler being called with -mfpmath=neon (or something alike) so it seems to be working next to VFPv2. > However, when you look at it like that, the option is not named correctly. What > the option is really about is specifying that the optional floating point/NEON > unit is indeed present. Here you have a good point. > Alternatively, if we really do want to support the case where only one of NEON > and VFPv3/4 is present, we should have a separate option similar to > BR2_ARM_ENABLE_NEON to enable the FPU. And in that case, of course, all the > MAYBEs should be removed from the Floating point strategy choice. Anyone has more available time than me to look into patching this? Would be greatly appreciated; would be using this for various customers of mine... See http://www.arm.com/Cortex-A9-chip-diagram-LG.png also. regards, Jaap Crezee
Jaap, Arnout, All, On 22 November 2015 at 00:16, Arnout Vandecappelle <arnout@mind.be> wrote: > On 21-11-15 20:53, Jaap Crezee wrote: >> Hi all, >> >> >> Can somebody please add the following (might not be completely right, that's why I post it >> like this): >> >> [jaap@jaap /data/work/zupr/git/buildroot ]$ git diff >> diff --git a/package/nodejs/Config.in b/package/nodejs/Config.in >> index 5128901..8d0ecad 100644 >> --- a/package/nodejs/Config.in >> +++ b/package/nodejs/Config.in >> @@ -32,7 +32,7 @@ config BR2_PACKAGE_NODEJS_V8_ARCH_SUPPORTS >> # On supported architectures other than ARM, no special requirement >> default y if !BR2_arm >> # On ARM, at least ARMv6+ with VFPv2+ is needed >> - default y if !BR2_ARM_CPU_ARMV5 && BR2_ARM_CPU_HAS_VFPV2 >> + default y if !BR2_ARM_CPU_ARMV5 && BR2_ARM_CPU_HAS_VFPV2 || BR2_ARM_CPU_HAS_NEON I was just about to submit a patch to bump node.js to v4.2.2. In v4.2.2 there is now a new --with-arm-fpu configure option (see https://github.com/nodejs/node/commit/17665af) which allows us to set the fpu to one of vfpv2, vfpv3, vfpv3-d16 or neon. Perhaps with this change it makes sense to have the || BR2_ARM_CPU_HAS_NEON since this is what the configure script will allow. The node.js Config.in is trying to say at a minimum we need vfpv2 i.e. it wants this default y if !BR2_ARM_CPU_ARMV5 && BR2_ARM_CPU_HAS_AT_LEAST_VFPV2 >> >> choice >> prompt "Node.js version" >> [jaap@jaap /data/work/zupr/git/buildroot ]$ >> >> To my oppinion Neon is a VFPv2 succesor. NodeJS builds and runs fine with Neon selected >> instead of VFPv2 for Cortex-A9. > > You have a good point. I don't think it's possible to have a NEON core without > VFP floating point unit. Hm, looking at [1], NEON and FPU are independently > optional, so theoretically you could have a Cortex-A9 with one but not the > other. But that probably doesn't exist in practice (in fact, we don't know any > Cortex-A9 that doesn't have both). > > However, I think it should be fixed in Config.in.arm instead. Basically, > whenever NEON is selected, the VFP's 'maybe' should be converted into a 'has'. > So something like > > --- a/arch/Config.in.arm > +++ b/arch/Config.in.arm > @@ -244,6 +244,9 @@ config BR2_ARM_ENABLE_NEON > bool "Enable NEON SIMD extension support" > depends on BR2_ARM_CPU_MAYBE_HAS_NEON > select BR2_ARM_CPU_HAS_NEON > + select BR2_ARM_CPU_HAS_VFPV3 if BR2_ARM_CPU_MAYBE_HAS_VFPV3 > + select BR2_ARM_CPU_HAS_VFPV4 if BR2_ARM_CPU_MAYBE_HAS_VFPV4 > help > For some CPU cores, the NEON SIMD extension is optional. > Select this option if you are certain your particular > > (Note that the VFPv2 cores never have NEON - at least as far as I know. Checked > arm.com and that seems to be correct.) The need for at least vfpv2 comes from googles v8 javascript engine that node.js uses. I found this comment in the V8 code https://github.com/nodejs/node/blob/master/deps/v8/src/base/cpu.cc#L526-L529 which says " ... neon is only available on architectures with vfpv3." and "... it is possible to have neon without vfp" which seems to make sense. Thanks Martin > > However, when you look at it like that, the option is not named correctly. What > the option is really about is specifying that the optional floating point/NEON > unit is indeed present. > > Alternatively, if we really do want to support the case where only one of NEON > and VFPv3/4 is present, we should have a separate option similar to > BR2_ARM_ENABLE_NEON to enable the FPU. And in that case, of course, all the > MAYBEs should be removed from the Floating point strategy choice. > > > Regards, > Arnout > > > [1] http://www.arm.com/products/processors/cortex-a/cortex-a9.php > -- > Arnout Vandecappelle arnout at mind be > Senior Embedded Software Architect +32-16-286500 > Essensium/Mind http://www.mind.be > G.Geenslaan 9, 3001 Leuven, Belgium BE 872 984 063 RPR Leuven > LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle > GPG fingerprint: 7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF
--- a/arch/Config.in.arm +++ b/arch/Config.in.arm @@ -244,6 +244,9 @@ config BR2_ARM_ENABLE_NEON bool "Enable NEON SIMD extension support" depends on BR2_ARM_CPU_MAYBE_HAS_NEON select BR2_ARM_CPU_HAS_NEON + select BR2_ARM_CPU_HAS_VFPV3 if BR2_ARM_CPU_MAYBE_HAS_VFPV3 + select BR2_ARM_CPU_HAS_VFPV4 if BR2_ARM_CPU_MAYBE_HAS_VFPV4 help For some CPU cores, the NEON SIMD extension is optional. Select this option if you are certain your particular