On Wed, Jan 24, 2018 at 02:00:42PM +0100, Geert Uytterhoeven wrote:

Hi Yury,

On Wed, Jan 24, 2018 at 10:05 AM, Yury Norov [off-list ref] wrote:

quoted

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 <redacted>

Thanks for your patch!

quoted

--- 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.

Shure, thanks.

Yury
 

quoted

+       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 at 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