linux-kernel - Re: [PATCH v2 3/8] ARM: tegra: rework Tegra secondary CPU core bringup

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Message-ID: <20120201110836.GB3058@mudshark.cambridge.arm.com>
Date:	Wed, 1 Feb 2012 11:08:36 +0000
From:	Will Deacon <will.deacon@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Peter De Schrijver <pdeschrijver@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Gary King <gking@...dia.com>, Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Colin Cross <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 3/8] ARM: tegra: rework Tegra secondary CPU core
 bringup

On Tue, Jan 31, 2012 at 10:50:45PM +0000, Russell King - ARM Linux wrote:
> On Tue, Jan 31, 2012 at 06:40:41PM +0200, Peter De Schrijver wrote:
> > +#ifdef CONFIG_ARM_ERRATA_743622
> > +	teq	r6, #0x20			@ present in r2p0
> > +	teqne	r6, #0x21			@ present in r2p1
> > +	teqne	r6, #0x22			@ present in r2p2
> > +	teqne	r6, #0x27			@ present in r2p7
> > +	teqne	r6, #0x29			@ present in r2p9
> 
> Okay, so we have this errata in proc-v7.S, but only for p0..p2.  If
> it's also p7 and p9, then it shows that the errata in the kernel aren't
> being actively maintained, and brings into question their worth.

It looks like the errata document has been updated since I wrote the
workaround in proc-v7.S (and new r2p* versions of the A9 have been
released). The new document states that r2p* are affected, so we should
update the workaround.

> Plus, of course, we don't want platforms re-implementing the errata
> in their own code if we're already implementing it somewhere in the
> kernel.  So, that's something which needs to be thought about.

Indeed, that could become extremely confusing, especially when they start
doing different things.

> That's something that needs considering along side the whole 'what
> to do about errata when running in non-secure mode' problem which
> OMAP suffers from.

My view is that the workarounds in the kernel are a good way to highlight
which errata we consider to be important from Linux's point-of-view and also
how to avoid them in practice. It's not always possible to apply them in the
kernel at runtime (due to security constraints) but I think it's important
to show what Linux expects.

I'll go back through the errata document and check if any others have been
updated besides this one.

Will
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