From: George Pee <georgepee@gmail.com> To: Robin Murphy <robin.murphy@arm.com> Cc: Russell King <linux@armlinux.org.uk>, "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>, Catalin Marinas <catalin.marinas@arm.com>, "Kirill A. Shutemov" <kirill.shtuemov@linux.intel.com>, Austin Kim <austindh.kim@gmail.com>, Ard Biesheuvel <ardb@kernel.org>, Mike Rapoport <rppt@kernel.org>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Report support for optional ARMv8.2 half-precision floating point extension Date: Fri, 9 Sep 2022 09:54:52 -0500 [thread overview] Message-ID: <CAKj0CMsEVOjz2TU+hA1kO181=i1KJsNX5SnEJvUajamgooivUg@mail.gmail.com> (raw) In-Reply-To: <28b35935-4e7f-2bd5-dda5-ed81402a527e@arm.com> That makes a lot of sense. How's this? Flipping the HWCAP2_FPHP bit is already in a CONFIG_VFPv3 check. diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h index 990199d8b7c6..5d635dce8853 100644 --- a/arch/arm/include/uapi/asm/hwcap.h +++ b/arch/arm/include/uapi/asm/hwcap.h @@ -37,5 +37,6 @@ #define HWCAP2_SHA1 (1 << 2) #define HWCAP2_SHA2 (1 << 3) #define HWCAP2_CRC32 (1 << 4) +#define HWCAP2_FPHP (1 << 5) #endif /* _UAPI__ASMARM_HWCAP_H */ diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index c39303e5c234..161f8df852e1 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -625,11 +625,12 @@ call_fpe: ret.w lr @ CP#6 ret.w lr @ CP#7 ret.w lr @ CP#8 - ret.w lr @ CP#9 #ifdef CONFIG_VFP + W(b) do_vfp @ CP#9 (VFP/FP16) W(b) do_vfp @ CP#10 (VFP) W(b) do_vfp @ CP#11 (VFP) #else + ret.w lr @ CP#9 ret.w lr @ CP#10 (VFP) ret.w lr @ CP#11 (VFP) #endif diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index 1e8a50a97edf..8887d0f447d6 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -1258,6 +1258,7 @@ static const char *hwcap2_str[] = { "sha1", "sha2", "crc32", + "fphp", NULL }; diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 2cb355c1b5b7..fb774fd5c614 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -831,6 +831,8 @@ static int __init vfp_init(void) if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000) elf_hwcap |= HWCAP_VFPv4; + if ((fmrx(MVFR1) & 0x0f000000) == 0x03000000) + elf_hwcap2 |= HWCAP2_FPHP; } /* Extract the architecture version on pre-cpuid scheme */ } else { On Fri, Sep 9, 2022 at 9:17 AM Robin Murphy <robin.murphy@arm.com> wrote: > > On 2022-09-09 14:34, George Pee wrote: > > Adding the hwcap was part of the diagnosis process-- I added it just > > to make sure that the cpu in question supported the optional > > extension. > > It seems like it could be useful to be able to check for support in > > /proc/cpuinfo. > > Sure, but "support" is about more than just what happens to be present > in hardware. Observe that you can build the 32-bit kernel with > CONFIG_VFP=n, and it then does not report and VFP or NEON hwcaps, > because those features will not be usable in that configuration, even if > you know the hardware implements them. > > Note that this looks different on arm64, since there we always expect to > have FPSIMD hardware available, so support in the kernel is > unconditional, plus that kernel support is also a lot simpler since we > don't have a soft-float ABI with all the corresponding trapping stuff > either. > > It might just be the case here that the call_fpe logic needs a bit of > tweaking to provide proper support, but I'm not sufficiently familiar > with the ARM VFP code in general to be sure. > > Thanks, > Robin. > > > On Fri, Sep 9, 2022 at 7:46 AM Robin Murphy <robin.murphy@arm.com> wrote: > >> > >> On 2022-09-01 15:13, george pee wrote: > >>> Report as fphp to be consistent with arm64 > >> > >> Wasn't the original problem that the VFP support code doesn't understand > >> the new FP16 instruction encodings, so in practice they don't actually > >> work reliably? Exposing a hwcap to say they're functional doesn't > >> inherently make them functional - if there is already another patch > >> somewhere for that, it should be made clear that this depends on it. > >> > >> Robin. > >> > >>> Signed-off-by: george pee <georgepee@gmail.com> > >>> --- > >>> arch/arm/include/uapi/asm/hwcap.h | 1 + > >>> arch/arm/kernel/setup.c | 1 + > >>> arch/arm/vfp/vfpmodule.c | 2 ++ > >>> 3 files changed, 4 insertions(+) > >>> > >>> diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h > >>> index 990199d8b7c6..f975845ce5d3 100644 > >>> --- a/arch/arm/include/uapi/asm/hwcap.h > >>> +++ b/arch/arm/include/uapi/asm/hwcap.h > >>> @@ -28,6 +28,7 @@ > >>> #define HWCAP_IDIV (HWCAP_IDIVA | HWCAP_IDIVT) > >>> #define HWCAP_LPAE (1 << 20) > >>> #define HWCAP_EVTSTRM (1 << 21) > >>> +#define HWCAP_FPHP (1 << 22) > >>> > >>> /* > >>> * HWCAP2 flags - for elf_hwcap2 (in kernel) and AT_HWCAP2 > >>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c > >>> index 1e8a50a97edf..6694ced0552a 100644 > >>> --- a/arch/arm/kernel/setup.c > >>> +++ b/arch/arm/kernel/setup.c > >>> @@ -1249,6 +1249,7 @@ static const char *hwcap_str[] = { > >>> "vfpd32", > >>> "lpae", > >>> "evtstrm", > >>> + "fphp", > >>> NULL > >>> }; > >>> > >>> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c > >>> index 2cb355c1b5b7..cef8c64ce8bd 100644 > >>> --- a/arch/arm/vfp/vfpmodule.c > >>> +++ b/arch/arm/vfp/vfpmodule.c > >>> @@ -831,6 +831,8 @@ static int __init vfp_init(void) > >>> > >>> if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000) > >>> elf_hwcap |= HWCAP_VFPv4; > >>> + if ((fmrx(MVFR1) & 0x0f000000) == 0x03000000) > >>> + elf_hwcap |= HWCAP_FPHP; > >>> } > >>> /* Extract the architecture version on pre-cpuid scheme */ > >>> } else {
WARNING: multiple messages have this Message-ID (diff)
From: George Pee <georgepee@gmail.com> To: Robin Murphy <robin.murphy@arm.com> Cc: Russell King <linux@armlinux.org.uk>, "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>, Catalin Marinas <catalin.marinas@arm.com>, "Kirill A. Shutemov" <kirill.shtuemov@linux.intel.com>, Austin Kim <austindh.kim@gmail.com>, Ard Biesheuvel <ardb@kernel.org>, Mike Rapoport <rppt@kernel.org>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Report support for optional ARMv8.2 half-precision floating point extension Date: Fri, 9 Sep 2022 09:54:52 -0500 [thread overview] Message-ID: <CAKj0CMsEVOjz2TU+hA1kO181=i1KJsNX5SnEJvUajamgooivUg@mail.gmail.com> (raw) In-Reply-To: <28b35935-4e7f-2bd5-dda5-ed81402a527e@arm.com> That makes a lot of sense. How's this? Flipping the HWCAP2_FPHP bit is already in a CONFIG_VFPv3 check. diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h index 990199d8b7c6..5d635dce8853 100644 --- a/arch/arm/include/uapi/asm/hwcap.h +++ b/arch/arm/include/uapi/asm/hwcap.h @@ -37,5 +37,6 @@ #define HWCAP2_SHA1 (1 << 2) #define HWCAP2_SHA2 (1 << 3) #define HWCAP2_CRC32 (1 << 4) +#define HWCAP2_FPHP (1 << 5) #endif /* _UAPI__ASMARM_HWCAP_H */ diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index c39303e5c234..161f8df852e1 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -625,11 +625,12 @@ call_fpe: ret.w lr @ CP#6 ret.w lr @ CP#7 ret.w lr @ CP#8 - ret.w lr @ CP#9 #ifdef CONFIG_VFP + W(b) do_vfp @ CP#9 (VFP/FP16) W(b) do_vfp @ CP#10 (VFP) W(b) do_vfp @ CP#11 (VFP) #else + ret.w lr @ CP#9 ret.w lr @ CP#10 (VFP) ret.w lr @ CP#11 (VFP) #endif diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index 1e8a50a97edf..8887d0f447d6 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -1258,6 +1258,7 @@ static const char *hwcap2_str[] = { "sha1", "sha2", "crc32", + "fphp", NULL }; diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 2cb355c1b5b7..fb774fd5c614 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -831,6 +831,8 @@ static int __init vfp_init(void) if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000) elf_hwcap |= HWCAP_VFPv4; + if ((fmrx(MVFR1) & 0x0f000000) == 0x03000000) + elf_hwcap2 |= HWCAP2_FPHP; } /* Extract the architecture version on pre-cpuid scheme */ } else { On Fri, Sep 9, 2022 at 9:17 AM Robin Murphy <robin.murphy@arm.com> wrote: > > On 2022-09-09 14:34, George Pee wrote: > > Adding the hwcap was part of the diagnosis process-- I added it just > > to make sure that the cpu in question supported the optional > > extension. > > It seems like it could be useful to be able to check for support in > > /proc/cpuinfo. > > Sure, but "support" is about more than just what happens to be present > in hardware. Observe that you can build the 32-bit kernel with > CONFIG_VFP=n, and it then does not report and VFP or NEON hwcaps, > because those features will not be usable in that configuration, even if > you know the hardware implements them. > > Note that this looks different on arm64, since there we always expect to > have FPSIMD hardware available, so support in the kernel is > unconditional, plus that kernel support is also a lot simpler since we > don't have a soft-float ABI with all the corresponding trapping stuff > either. > > It might just be the case here that the call_fpe logic needs a bit of > tweaking to provide proper support, but I'm not sufficiently familiar > with the ARM VFP code in general to be sure. > > Thanks, > Robin. > > > On Fri, Sep 9, 2022 at 7:46 AM Robin Murphy <robin.murphy@arm.com> wrote: > >> > >> On 2022-09-01 15:13, george pee wrote: > >>> Report as fphp to be consistent with arm64 > >> > >> Wasn't the original problem that the VFP support code doesn't understand > >> the new FP16 instruction encodings, so in practice they don't actually > >> work reliably? Exposing a hwcap to say they're functional doesn't > >> inherently make them functional - if there is already another patch > >> somewhere for that, it should be made clear that this depends on it. > >> > >> Robin. > >> > >>> Signed-off-by: george pee <georgepee@gmail.com> > >>> --- > >>> arch/arm/include/uapi/asm/hwcap.h | 1 + > >>> arch/arm/kernel/setup.c | 1 + > >>> arch/arm/vfp/vfpmodule.c | 2 ++ > >>> 3 files changed, 4 insertions(+) > >>> > >>> diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h > >>> index 990199d8b7c6..f975845ce5d3 100644 > >>> --- a/arch/arm/include/uapi/asm/hwcap.h > >>> +++ b/arch/arm/include/uapi/asm/hwcap.h > >>> @@ -28,6 +28,7 @@ > >>> #define HWCAP_IDIV (HWCAP_IDIVA | HWCAP_IDIVT) > >>> #define HWCAP_LPAE (1 << 20) > >>> #define HWCAP_EVTSTRM (1 << 21) > >>> +#define HWCAP_FPHP (1 << 22) > >>> > >>> /* > >>> * HWCAP2 flags - for elf_hwcap2 (in kernel) and AT_HWCAP2 > >>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c > >>> index 1e8a50a97edf..6694ced0552a 100644 > >>> --- a/arch/arm/kernel/setup.c > >>> +++ b/arch/arm/kernel/setup.c > >>> @@ -1249,6 +1249,7 @@ static const char *hwcap_str[] = { > >>> "vfpd32", > >>> "lpae", > >>> "evtstrm", > >>> + "fphp", > >>> NULL > >>> }; > >>> > >>> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c > >>> index 2cb355c1b5b7..cef8c64ce8bd 100644 > >>> --- a/arch/arm/vfp/vfpmodule.c > >>> +++ b/arch/arm/vfp/vfpmodule.c > >>> @@ -831,6 +831,8 @@ static int __init vfp_init(void) > >>> > >>> if ((fmrx(MVFR1) & 0xf0000000) == 0x10000000) > >>> elf_hwcap |= HWCAP_VFPv4; > >>> + if ((fmrx(MVFR1) & 0x0f000000) == 0x03000000) > >>> + elf_hwcap |= HWCAP_FPHP; > >>> } > >>> /* Extract the architecture version on pre-cpuid scheme */ > >>> } else { _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-09-09 14:55 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-01 14:13 [PATCH] Report support for optional ARMv8.2 half-precision floating point extension george pee 2022-09-01 14:13 ` george pee 2022-09-09 11:39 ` Catalin Marinas 2022-09-09 11:39 ` Catalin Marinas 2022-09-09 13:35 ` George Pee 2022-09-09 13:35 ` George Pee 2022-09-09 12:46 ` Robin Murphy 2022-09-09 12:46 ` Robin Murphy 2022-09-09 13:34 ` George Pee 2022-09-09 13:34 ` George Pee 2022-09-09 14:07 ` Catalin Marinas 2022-09-09 14:07 ` Catalin Marinas 2022-09-09 14:57 ` George Pee 2022-09-09 14:57 ` George Pee 2022-09-09 15:05 ` Catalin Marinas 2022-09-09 15:05 ` Catalin Marinas 2022-09-12 13:05 ` Russell King (Oracle) 2022-09-12 13:05 ` Russell King (Oracle) 2022-09-12 18:09 ` George Pee 2022-09-12 18:09 ` George Pee 2022-09-09 14:17 ` Robin Murphy 2022-09-09 14:17 ` Robin Murphy 2022-09-09 14:54 ` George Pee [this message] 2022-09-09 14:54 ` George Pee
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