linux-kernel - Re: [PATCH 1/1] MIPS: Add new Kconfig variable to avoid unaligned access instructions

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Message-ID: <a75bc7c92bd9806a56ec2736218dec15b5cf7eba.camel@gmail.com>
Date:   Tue, 25 Sep 2018 23:12:53 +0300
From:   Yasha Cherikovsky <yasha.che3@...il.com>
To:     Paul Burton <paul.burton@...s.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] MIPS: Add new Kconfig variable to avoid unaligned
 access instructions

On Tue, 2018-09-25 at 19:57 +0000, Paul Burton wrote:
> Hi Yasha,
> 
> On Tue, Sep 25, 2018 at 10:30:52PM +0300, Yasha Cherikovsky wrote:
> > On Tue, 2018-09-25 at 17:45 +0000, Paul Burton wrote:
> > > How about we:
> > > 
> > >   - Add a Kconfig option CONFIG_CPU_SUPPORTS_LOAD_STORE_LR, and
> > > select
> > >     it for all existing pre-r6 targets (probably from CONFIG_CPU_*).
> > > 
> > >   - Change CONFIG_GENERIC_CSUM to default y if
> > >     !CONFIG_CPU_SUPPORTS_LOAD_STORE_LR, and drop the selects of it.
> > > 
> > > That would avoid the double-negative ("if we don't not support this")
> > > that the #ifndef's currently represent. It would also mean any future
> > > architecture/ISA targets beyond MIPSr6 automatically avoid the
> > > instructions.
> > 
> > Thanks for your feedback, I'll start preparing v2.
> > 
> > Looking in arch/mips/Kconfig, some CPU options start
> > with CPU_SUPPORTS_ and some with CPU_HAS_.
> > Which perfix should we use here?
> 
> That's a good question :)
> 
> To be honest I don't think either of them is perfect, since what we're
> really describing is what's supported by the ISA that the kernel build
> is targeting - and in theory the CPU we actually run on could support
> extra things.
> 
> But considering it I think CPU_HAS_ is probably the best choice for
> this, since it's already used similarly to indicate support for pref &
> sync instructions.
> 
> Thanks,
>     Paul

OK, Thanks.