linux-kernel - Re: [PATCH V3 14/22] LoongArch: Add signal handling support

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Message-ID: <a0fb870d-3b79-ca77-305f-6178974729e4@twiddle.net>
Date:   Mon, 20 Sep 2021 14:14:10 -0700
From:   Richard Henderson <rth@...ddle.net>
To:     Huacai Chen <chenhuacai@...il.com>, Arnd Bergmann <arnd@...db.de>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V3 14/22] LoongArch: Add signal handling support

On 9/19/21 7:36 PM, Huacai Chen wrote:
> Hi, Arnd,
> 
> On Sun, Sep 19, 2021 at 5:59 PM Arnd Bergmann <arnd@...db.de> wrote:
>>
>> On Sat, Sep 18, 2021 at 9:12 AM Huacai Chen <chenhuacai@...il.com> wrote:
>>> On Sat, Sep 18, 2021 at 5:10 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>>>> For example does LoongArch have a version without built in floating
>>>> point support?
>>>
>>> Some of these structures seems need rethinking, But we really have
>>> LoongArch-based MCUs now (no FP, no SMP, and even no MMU).
>>
>> NOMMU Linux is kind-of on the way out as interest is fading, so I hope you
>> don't plan on supporting this in the future.
>>
>> Do you expect to see future products with MMU but no FP or no SMP?
> OK, we will not care no-MMU hardware in Linux, but no-FP and no-SMP
> hardware will be supported.

Please consider requiring the FP registers to be present even on no-FP hardware.

With this plus the FP data movement instructions (FMOV, MOVGR2FR, MOVFR2GR, FLD, FST), it 
is possible to implement soft-float without requiring a separate soft-float ABI.  This can 
vastly simplify compatibility and deployment.


r~