linux-kernel - Re: [PATCH] MIPS: Introduce aligned IO memory operations

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Message-ID: <20200124140751.GA17030@alpha.franken.de>
Date:   Fri, 24 Jan 2020 15:07:51 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Paul Burton <paulburton@...nel.org>
Cc:     Jiaxun Yang <jiaxun.yang@...goat.com>, linux-mips@...r.kernel.org,
        chenhc@...ote.com, paul.burton@...s.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Introduce aligned IO memory operations

On Wed, Jan 22, 2020 at 10:45:06AM -0800, Paul Burton wrote:
> Hi Jiaxun,
> 
> On Tue, Jan 14, 2020 at 08:23:43PM +0800, Jiaxun Yang wrote:
> > Some platforms, such as Loongson64 or QEMU/KVM, don't support unaligned
> > instructions like lwl or lwr in IO memory access. However, our current
> > IO memcpy/memset is wired to the generic implementation, which leads
> > to a fatal result.
> 
> Hmm, I wonder if we should just do this unconditionally on all systems.
> I can't think of a reason it'd ever be a good idea to use lwl/lwr on an
> MMIO device. Any thoughts on that?

depends on the type of device. I can see benefits for framebuffers
and memory devices since memset/memcpy are more optimised than the
function in this patch.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]