Re: [PATCH RFC 0/3] API for 128-bit IO access

From: Robin Murphy
Date: Thu Jan 25 2018 - 07:11:24 EST

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In reply to: Yury Norov: "Re: [PATCH RFC 0/3] API for 128-bit IO access"
Next in thread: Arnd Bergmann: "Re: [PATCH RFC 0/3] API for 128-bit IO access"
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On 25/01/18 11:38, Yury Norov wrote:

On Wed, Jan 24, 2018 at 11:28:55AM +0100, Arnd Bergmann wrote:

On Wed, Jan 24, 2018 at 10:05 AM, Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> wrote:

This series adds API for 128-bit memory IO access and enables it for ARM64.
The original motivation for 128-bit API came from new Cavium network device
driver. The hardware requires 128-bit access to make things work. See
description in patch 3 for details.

We might also want to do something similar to the
include/linux/io-64-nonatomic-lo-hi.h
and hi-lo.h files, to simulate 128-bit access using pairs of 64-bit access on
other targets. It's apparently driver specific which half you need to do first
to make it work, so we need both.

OK, will do.

Also, starting from ARMv8.4, stp and ldp instructions become atomic, and
API for 128-bit access would be helpful in core arm64 code.

This series is RFC. I'd like to collect opinions on idea and implementation
details.
* I didn't implement all 128-bit operations existing for 64-bit variables
and other types (__swab128p etc). Do we need them all right now, or we
can add them when actually needed?

I think in this case it's better to do them all at once.

Ack.

* u128 name is already used in crypto code. So here I use __uint128_t that
comes from GCC for 128-bit types. Should I rename existing type in crypto
and make core code for 128-bit variables consistent with u64, u32 etc? (I
think yes, but would like to ask crypto people for it.)

Hmm, that file probably predates the __uint128_t support. My guess would
be that the crypto code using it can actually benefit from the new types as
well, so maybe move the existing file to include/linux/int128.h and add
an #if/#else logic to it so we use 'typedef __uint128_t __u128' if that
is available.

It sounds reasonable. But I worry about testing that changes. Hope,
crypto community will help with it.

* Some compilers don't support __uint128_t, so I protected all generic code
with config option HAVE_128BIT_ACCESS. I think it's OK, but...

That would be nicely solved by using the #if/#else definition above.

* For 128-bit read/write functions I take suffix 'o', which means read/write
the octet of bytes. Is this name OK?

Can't think of anything better. It's not an octet though, but 16 bytes
('q' is for quadword, meaning four 16-bit words in Intel terminology).

Ah, sure. Octet of words. Will change it.

* my mips-linux-gnu-gcc v6.3.0 doesn't support __uint128_t, and I
don't have other BE setup on hand, so BE case is formally not tested.
BE code for arm64 is looking well though.

I've run it through my collection of compilers, it seems that most but not
all 64-bit targets support it (exceptions appear to be older versions of
gcc for s390x and parisc), and none of the 32-bit targets do:

Thanks for doing this test. Looking at this I realize that this is
not the architecture feature but compiler feature. So if we add
128-bit interface, it would be reasonable to add it for all targets
that compiled with toolchain supporting 128-bit accesses.

There's already the option ARCH_SUPPORTS_INT128 that is enabled for
x86_64 in arch/x86/Kconfig and conditionally enabled for arm64 in
arch/arm64/Makefile:
KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)

It is used in include/linux/math64.h and in lib/ubsan.c, not so wide.

So I find things little messed. Crypto code ignores compilers' ability
to operate with 128-bit numbers. Ubsan and math64 relies on compiler
version (at least for arm64, and I doubt it would work correctly with clang).
And now I introduce HAVE_128BIT_ACCESS with the same meaning for memory
access.

I think it's time to unify 128-bit code:
- enable CONFIG_ARCH_SUPPORTS_INT128 if compiler supports it, ie check
it like you do below;
- declare u128 as structure or typedef depending on ARCH_SUPPORTS_INT128
in generic include/linux/int128.h, as you suggest here;
- switch this series to ARCH_SUPPORTS_INT128.

Does it sound reasonable?

It probably is about time to formalise the current scattered fragments of uint_128_t support, but to reiterate Will's comment it is almost certainly not worth the effort to implement 'generic' I/O accessors which only work under implementation-defined and undiscoverable hardware conditions, and will be unusable on the overwhelming majority of systems. Just open-code LDP/STP accessors in the one driver which needs them and (by definition) only runs on SoCs where they *are* known to work correctly.

Robin.

Yury

$ for i in /home/arnd/cross-gcc/bin/*gcc-[3-8]* ; do echo -n $i" " ;
echo '__uint128_t v;' | $i -xc -S - -o /dev/null && echo ok ; done
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-4.8.5 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-4.9.3 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-4.9.4 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-5.2.1 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-5.4.1 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-5.5.0 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-6.3.1 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-7.0.0 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-7.0.1 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-7.1.1 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/aarch64-linux-gcc-8.0.0 ok
/home/arnd/cross-gcc/bin/alpha-linux-gcc-4.1.3 ok
/home/arnd/cross-gcc/bin/alpha-linux-gcc-4.3.6 ok
/home/arnd/cross-gcc/bin/alpha-linux-gcc-4.9.3 ok
/home/arnd/cross-gcc/bin/alpha-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/am33_2.0-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/am33_2.0-linux-gcc-5.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/am33_2.0-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/arc-elf-gcc-7.2.1 <stdin>:1:1: error: unknown
type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-3.4.6 ok
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.4.7 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.5.4 <stdin>:1:13:
error: expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.6.4 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.7.4 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.8.5 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.9.0 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.9.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.9.2 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.9.3 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-4.9.4 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-5.0.0 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-5.1.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-5.2.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-5.3.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-5.4.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-5.5.0 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-6.0.0 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-6.1.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-6.3.1 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-7.0.0 <stdin>:1:1:
error: unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-7.0.1 <stdin>:1:1:
error: unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-7.1.1 <stdin>:1:1:
error: unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-7.2.1 <stdin>:1:1:
error: unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/arm-linux-gnueabi-gcc-8.0.0 <stdin>:1:1:
error: unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/bfin-uclinux-gcc-7.0.0
bfin-uclinux-gcc-7.0.0: error trying to exec 'cc1': execvp: No such
file or directory
/home/arnd/cross-gcc/bin/bfin-uclinux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/c6x-elf-gcc-7.2.1 <stdin>:1:1: error: unknown
type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/cris-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/cris-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/cris-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/cris-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/frv-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/frv-linux-gcc-4.3.6 <stdin>:1: internal
compiler error: in default_secondary_reload, at targhooks.c:618
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
/home/arnd/cross-gcc/bin/frv-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/frv-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/h8300-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/hppa64-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/hppa64-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/hppa-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/hppa-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/hppa-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/hppa-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/i386-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/i386-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/ia64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/m32r-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/m32r-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/m32r-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/m32r-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/m68k-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/m68k-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/m68k-linux-gcc-6.0.0 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/m68k-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/microblaze-linux-gcc-4.9.3 <stdin>:1:1:
error: unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/microblaze-linux-gcc-7.2.1 <stdin>:1:1:
error: unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/mips64-linux-gcc-4.9.3 ok
/home/arnd/cross-gcc/bin/mips64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/mips-linux-gcc-4.0.4 <stdin>:1: error: syntax
error before 'v'
<stdin>:1: warning: data definition has no type or storage class
/home/arnd/cross-gcc/bin/mips-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/mips-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/mips-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/mips-linux-gcc-7.0.0 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/mips-linux-gcc-7.0.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/mips-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/nios2-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/parisc-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/powerpc64-linux-gcc-4.1.3 ok
/home/arnd/cross-gcc/bin/powerpc64-linux-gcc-4.3.6 ok
/home/arnd/cross-gcc/bin/powerpc64-linux-gcc-4.9.3 ok
/home/arnd/cross-gcc/bin/powerpc64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/powerpc-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/powerpc-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/riscv32-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/riscv64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/s390-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/s390-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/s390-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/s390-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/sh2-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/sh3-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/sh3-linux-gcc-4.3.6 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/sh3-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/sh4-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/sh-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/sparc64-linux-gcc-4.9.3 ok
/home/arnd/cross-gcc/bin/sparc64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/sparc-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/sparc-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/sparc-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/tilegx-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/tilepro-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-3.4.6 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.0.4 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.1.3 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.2.5 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.3.6 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.4.7 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.5.4 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.6.4 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.7.4 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.8.5 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.9.3 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-4.9.4 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-5.4.1 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-5.5.0 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-6.1.1 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-6.3.1 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-7.0.0 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-7.0.1 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-7.1.1 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-7.2.1 ok
/home/arnd/cross-gcc/bin/x86_64-linux-gcc-8.0.0 ok
/home/arnd/cross-gcc/bin/xtensa-linux-gcc-4.1.3 <stdin>:1: error:
expected '=', ',', ';', 'asm' or '__attribute__' before 'v'
/home/arnd/cross-gcc/bin/xtensa-linux-gcc-4.9.3 <stdin>:1:1: error:
unknown type name '__uint128_t'
/home/arnd/cross-gcc/bin/xtensa-linux-gcc-7.2.1 <stdin>:1:1: error:
unknown type name '__uint128_t'; did you mean '__int128'?

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