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

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Date:   Tue, 16 Oct 2018 13:35:44 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     Stefan Agner <stefan@...er.ch>,
        Hans Ulli Kroll <ulli.kroll@...glemail.com>,
        Joel Stanley <joel@....id.au>, Nicolas Pitre <nico@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Roman Yeryomin <roman@...em.lv>
Subject: Re: [PATCH 1/2] ARM: copypage-fa: add kto and kfrom to input operands list

On Tue, Oct 16, 2018 at 10:44 AM Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Tue, Oct 16, 2018 at 10:00:19AM +0200, Linus Walleij wrote:

> > I am on deep waters with ARM assembly, admittedly. So I wanted to
> > ask: OpenWRT has this cache patch:
> > https://github.com/openwrt/openwrt/blob/master/target/linux/gemini/patches-4.14/0001-cache-patch-from-OpenWRT.patch
> > I do not know why (sorry).
> >
> > Do you think that patch is actually a hack to hide the problem
> > fixed with this patch? (OK maybe stupid question but...)
>
> No, it looks to me like a hack to make DMA cache handling "more
> efficient" by cleaning/invalidating the entire cache when dealing
> with large streaming buffers.

Aha that makes a lot of sense.

I will attempt to drop it from OpenWRT in the next kernel upgrade
unless benchmarks can show that it is worth it.

Thanks Russell!

Linus Walleij