linux-kernel - Re: [PATCH v2] ARM : Support for optional ARMv8.2 half-precision floating point extension

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Date:   Thu, 3 Nov 2022 17:18:21 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     george pee <georgepee@...il.com>, Mark Brown <broonie@...nel.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Keith Packard <keithpac@...zon.com>,
        Austin Kim <austindh.kim@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ARM : Support for optional ARMv8.2 half-precision
 floating point extension

Sorry for top-posting but provding context.

Please CC Mark Brown om FP extensions, he is looking after these.
Now add on To:

Yours,
Linus Walleij

On Mon, Sep 12, 2022 at 3:25 PM george pee <georgepee@...il.com> wrote:

> Report feature /proc/cpuinfo as fphp to be consistent with arm64
>
> Signed-off-by: george pee <georgepee@...il.com>
> ---
>  arch/arm/include/uapi/asm/hwcap.h | 1 +
>  arch/arm/kernel/entry-armv.S      | 3 ++-
>  arch/arm/kernel/setup.c           | 1 +
>  arch/arm/vfp/vfpmodule.c          | 2 ++
>  4 files changed, 6 insertions(+), 1 deletion(-)
>
> 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..0806b0b1f2c7 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 {
> --
> 2.37.3
>