From: "Thomas Weißschuh" <linux@weissschuh.net>
To: Xi Ruoyao <xry111@xry111.site>
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, 2 Apr 2026 08:39:13 +0200 [thread overview]
Message-ID: <b484cc9e-3582-41bf-bf5e-0a432e74a8f4@t-8ch.de> (raw)
In-Reply-To: <20260402044732.164294-2-xry111@xry111.site>
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.
> + "beqz\t%[tmp], 1b"
> + : [mem] "=ZB" (mem), [tmp] "=&r" (tmp)
> + : [one] "r" (1));
> +
> + if (mem.word[1] != 1) {
> + pr_warn_once("Warning: sc.q is erratic on this platform, disabling for both kernel and HWCAP. Please try a firmware update.");
> + return false;
> + }
> +
> + return true;
> +}
next prev parent reply other threads:[~2026-04-02 6:39 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 [this message]
2026-04-02 8:05 ` Xi Ruoyao
2026-04-07 15:21 ` kernel test robot
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