From: Xi Ruoyao <xry111@xry111.site>
To: "Thomas Weißschuh" <linux@weissschuh.net>
Cc: Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
loongarch@lists.linux.dev, Zixing Liu <liushuyu@aosc.io>,
Mingcong Bai <jeffbai@aosc.io>,
Jiaxun Yang <jiaxun.yang@flygoat.com>,
Arnd Bergmann <arnd@arndb.de>,
Yangyang Lian <lianyangyang@kylinos.cn>,
Yawei Li <liyawei@loongson.cn>,
George Guo <dongtai.guo@linux.dev>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] LoongArch: detect and disable sc.q if erratic
Date: Thu, 02 Apr 2026 16:05:05 +0800 [thread overview]
Message-ID: <6c9662c0f45131d8aa607d6962cb4237d3c7f129.camel@xry111.site> (raw)
In-Reply-To: <b484cc9e-3582-41bf-bf5e-0a432e74a8f4@t-8ch.de>
On Thu, 2026-04-02 at 08:39 +0200, Thomas Weißschuh wrote:
> On 2026-04-02 12:47:30+0800, Xi Ruoyao wrote:
>
> (...)
>
> > +/*
> > + * Some LoongArch has broken sc.q which incorrectly handles the upper word
> > + * when the lower word is zero. Newer firmware versions (such as the 202602
> > + * release from Loongson) seem to contain a workaround for this issue.
> > + *
> > + * Disable sc.q if erratic to ensure reliability and compatibility.
> > + */
> > +static bool sc_q_is_sane(void)
> > +{
> > + struct {
> > + long word[2];
> > + } __aligned(16) mem;
> > + register long tmp;
> > +
> > + asm (
> > + "1:ll.d\t$r0, %[mem]\n\t"
> > + "move\t%[tmp], $r0\n\t"
> > + "sc.q\t%[tmp], %[one], %[mem]\n\t"
>
> This probably needs to be gated behind CONFIG_AS_HAS_SCQ_EXTENSION to
> avoid errors on older toolchains.
I guess I'd code the insn with .word instead...
This also affects HWCAP, and I don't want the userspace to see neither a
false positive nor a false negative simply because the kernel was built
with an old toolchain.
--
Xi Ruoyao <xry111@xry111.site>
next prev parent reply other threads:[~2026-04-02 8:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-02 4:47 [PATCH] LoongArch: detect and disable sc.q if erratic Xi Ruoyao
2026-04-02 5:10 ` Mingcong Bai
2026-04-02 6:39 ` Thomas Weißschuh
2026-04-02 8:05 ` Xi Ruoyao [this message]
2026-04-07 15:21 ` kernel test robot
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