linux-kernel - Re: [PATCH] Remove ARM errata Workarounds 458693 and 460075

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Message-ID: <20170502152105.GC29224@e104818-lin.cambridge.arm.com>
Date:   Tue, 2 May 2017 16:21:05 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        dianders@...omium.org, vladimir.murzin@....com,
        Nisal Menuka <nisalmenuka23@...il.com>,
        kever.yang@...k-chips.com, linux-kernel@...r.kernel.org,
        armlinux@...isordat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] Remove ARM errata Workarounds 458693 and 460075

On Tue, May 02, 2017 at 01:27:54PM +0100, Robin Murphy wrote:
> On 18/04/17 16:57, Catalin Marinas wrote:
> > On Sun, Apr 16, 2017 at 09:04:46AM +0100, Russell King - ARM Linux wrote:
> >> On Sat, Apr 15, 2017 at 07:06:06PM -0500, Nisal Menuka wrote:
> >>> According to ARM, these errata exist only in a version of Cortex-A8
> >>> (r2p0) which was never built. Therefore, I believe there are no platforms
> >>> where this workaround should be enabled.
> >>> link :http://infocenter.arm.com/help/index.jsp?topic=
> >>> /com.arm.doc.faqs/ka15634.html
> >>
> >> These were submitted by ARM Ltd back in 2009 - if the silicon was never
> >> built, there would've been no reason to submit them.  Maybe Catalin can
> >> shed some light on this, being the commit author who introduced these?
> > 
> > We normally try not to submit errata workarounds for revisions that are
> > not going to be built/deployed. It's possible that at the time there
> > were plans for r2p0 to be licensed and built (not just FPGA) but I don't
> > really remember the details. The A8 errata document indeed states that
> > r1p0 and r2p0 are obsolete but this can mean many things (like not
> > available to license).
> > 
> > I'll try to see if any of the A8 past product managers know anything
> > about this. In the meantime, I would leave them in (no run-time
> > overhead).
> 
> FWIW, I just fired up a RealView PB-A8 board to check, and that reports
> r1p1. True, it's not strictly a real silicon implementation (I think
> it's one of the structured ASIC test chips), but since it was, as far as
> I'm aware, a commercially-available development system, it's not
> impossible that someone may still own and use one of these beasts.

The above errata were specific to r1p0 (not r1p1) and r2p0. Since ARM
Ltd claims there are no products built around these revisions, I'm fine
with removing the workarounds from the kernel (internal testchips/FPGA
don't count as products but I doubt they are still relevant 8 years
later).

-- 
Catalin