From: Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH 3/3] arm64: enable 128-bit memory read/write support
Date: Wed, 24 Jan 2018 14:00:42 +0100
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References: <20180124090519.6680-1-ynorov@caviumnetworks.com> <20180124090519.6680-4-ynorov@caviumnetworks.com>
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To: Yury Norov <ynorov@caviumnetworks.com>
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Hi Yury,

On Wed, Jan 24, 2018 at 10:05 AM, Yury Norov <ynorov@caviumnetworks.com> wrote:
> Introduce __raw_writeo(), __raw_reado() and other arch-specific
> RW functions for 128-bit memory access, and enable it for arm64.
>
> 128-bit I/O is required for example by Octeon TX2 device to access
> some registers. According to Hardware Reference Manual:
>
> A 128-bit write to the OP_FREE0/1 registers frees a pointer into a
> given [...] pool. All other accesses to these registers (e.g. reads
> and 64-bit writes) are RAZ/WI.
>
> Starting from ARMv8.4, stp and ldp instructions become atomic, and
> API for 128-bit access would be helpful for core code.
>
> Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>

Thanks for your patch!

> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -116,6 +116,13 @@ config UPROBES
>             managed by the kernel and kept transparent to the probed
>             application. )
>
> +config HAVE_128BIT_ACCESS
> +       def_bool ARM64

I think it's better to select this symbol from arch/arm64/Kconfig instead.
Else this file has to be modified each and every time an architecture
adds support for 128-bit, causing conflicts.

> +       help
> +         Architectures having 128-bit access require corresponding APIs,
> +         like reado() and writeo(), which stands for reading and writing
> +         the octet of bytes at once.
> +
>  config HAVE_64BIT_ALIGNED_ACCESS
>         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
>         help

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds