[MIPS] GCC: Fix Loongson3 LLSC Errata

[Jiaxun Yang]

On 2018/11/30 下午8:45, Paul Hua wrote:
> In some older Loongson3 processors there is a LL/SC errata that can
> cause the CPU to deadlock occasionally.  The details are very
> complicated. We find a way to work around this errata by a) adding a
> sync before ll/lld instruction, b) adding a sync
> before branch target that between ll and sc. The assembler do the jobs
> 'a', gcc do the jobs 'b'.

Hi all,

Any update about this patch?

As this workaround is the last barrier for generic MIPS distros to run 
on Loongson systems.

Btw, I heard from Loongson guys that type A (adding a sync before ll/lld 
instruction) of this errata only exist on pre-3A2000 (GS464) processors 
while type B exist on all processors. Is that true?

If so, then they should have different naming in flags to prevent 
confusing. I saw that you are using "LLTGT" and "LLSYNC" in cpucfg bit 
domin of 3A4000, should we also use that naming in toolchain?


Thanks.

--

Jiaxun Yang

> This patch also add a configure options
> --with-mips-fix-loongson3-llsc=[yes|no] to enable fix-loongson3-llsc
> by config.
>
> >From 16f0fd9e32d2098637dc0eb3e576444c48c43f22 Mon Sep 17 00:00:00 2001
> From: Chenghua Xu <paul.hua.gm@gmail.com>
> Date: Fri, 30 Nov 2018 19:57:38 +0800
> Subject: [PATCH] [MIPS][GCC]  Fix Loongson3 LLSC Errata.
>
> gcc/
> 	* config.gcc (supported_defaults): Add fix-loongson3-llsc
> 	(with_fix_loongson3_llsc): Add validation.
> 	(all_defaults): Add fix-loongson3-llsc.
> 	* config/mips/mips.c (mips_process_sync_loop): Add sync before
> 	branch target that between ll and sc.
> 	* config/mips/mips.h (OPTION_DEFAULT_SPECS): Add a default for
> 	fix-loongson3-llsc.
> 	gcc/config/mips/mips.opt: New option.
> 	* doc/install.texi (--with-fix-loongson3-llsc):Document the new
> 	option.
> 	* doc/invoke.texi (-mfix-loongson3-llsc):Document the new option.
>
> gcc/testsuite/
> 	* gcc.target/mips/fix-loongson3-llsc.c: New test.
> 	* gcc.target/mips/mips.exp (option): Add fix-loongson3-llsc.
> ---
>   gcc/config.gcc                                | 19 +++++++++++++++++--
>   gcc/config/mips/mips.c                        | 13 +++++++++++--
>   gcc/config/mips/mips.h                        |  4 +++-
>   gcc/config/mips/mips.opt                      |  4 ++++
>   gcc/doc/install.texi                          |  4 ++++
>   gcc/doc/invoke.texi                           |  8 ++++++++
>   .../gcc.target/mips/fix-loongson3-llsc.c      | 10 ++++++++++
>   gcc/testsuite/gcc.target/mips/mips.exp        |  1 +
>   8 files changed, 58 insertions(+), 5 deletions(-)
>   create mode 100644 gcc/testsuite/gcc.target/mips/fix-loongson3-llsc.c