linux-kernel - Re: [PATCH v6 5/9] dt-bindings: ARM: document marvell,ecc-enable binding

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Message-ID: <CAK8P3a26XmBpG3VzwUgSdd_Xo_S2ezSvA9mjKckRFr9p38j-dg@mail.gmail.com>
Date:   Fri, 9 Nov 2018 16:58:24 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Chris Packham <chris.packham@...iedtelesis.co.nz>,
        Borislav Petkov <bp@...en8.de>, jlu@...gutronix.de,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        DTML <devicetree@...r.kernel.org>, linux-edac@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v6 5/9] dt-bindings: ARM: document marvell,ecc-enable binding

On Fri, Nov 9, 2018 at 12:48 PM Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
>
> On Fri, Nov 09, 2018 at 12:40:06PM +0100, Arnd Bergmann wrote:
> > On Fri, Nov 9, 2018 at 8:04 AM Chris Packham
> > <chris.packham@...iedtelesis.co.nz> wrote:
> > >
> > > Add documentation for the marvell,ecc-enable and marvell,ecc-disable
> > > properties which can be used to enable/disable ECC on the Marvell aurora
> > > cache.
> > >
> > > Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> > > ---
> >
> > Why do you need both enable and disable? Wouldn't one of them be enough here?
>
> It isn't an "on when ecc-enable is present, off when not" because the
> current behaviour is to preserve these bits in the control register.
>
> If we were to implement it as "if no ecc-enable property, turn off
> ECC" then that would drastically change the behaviour - systems which
> were configured for ECC suddenly lose ECC support.
>
> Since we don't know which have it and which don't, we can't implement
> the option like that.

What I meant was why we need support force-disabling it. I understand
that we need to allow leaving it at the boot-time default as well as
force-enabling it.

       Arnd