linux-kernel - Re: [PATCH 1/2] ARM: copypage-fa: add kto and kfrom to input operands list

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Date:   Tue, 6 Nov 2018 08:25:12 -0500 (EST)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Robin Murphy <robin.murphy@....com>
cc:     Stefan Agner <stefan@...er.ch>, Arnd Bergmann <arnd@...db.de>,
        Roman Yeryomin <roman@...em.lv>,
        Linus Walleij <linus.walleij@...aro.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Joel Stanley <joel@....id.au>,
        Hans Ulli Kroll <ulli.kroll@...glemail.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] ARM: copypage-fa: add kto and kfrom to input operands
 list

On Tue, 6 Nov 2018, Robin Murphy wrote:

> On 06/11/2018 04:49, Nicolas Pitre wrote:
> [...]
> >> r3 and r5 are not used above, so no need to have them in the clobber
> >> list.
> > 
> > They are used. ldrd and strd instructions always use a pair of
> > consecutive registers. So "ldrd r2, ..." loads into r2-r3 and "ldrd r4, ..."
> > loads into r4-r5.
> 
> FWIW, since we should now be enabling unified syntax everywhere, I guess we
> could probably rewrite all those ldrd/strd to the UAL 3-operand form - i.e.
> "ldrd r2, r3, [...]" - if we really cared for the extra clarity.

Good idea. Worthy of a separate patch though.


Nicolas