From mboxrd@z Thu Jan  1 00:00:00 1970
From: marc.zyngier@arm.com (Marc Zyngier)
Date: Fri, 8 Apr 2016 11:24:09 +0100
Subject: [PATCH] arm64: erratum: Workaround for Kryo reserved system
 register read
In-Reply-To: <570780D2.3060104@arm.com>
References: <1460044456-5297-1-git-send-email-nkaje@codeaurora.org>
 <57069977.5050205@arm.com> <570780D2.3060104@arm.com>
Message-ID: <570786C9.6020804@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 08/04/16 10:58, Suzuki K Poulose wrote:
> On 07/04/16 18:31, Marc Zyngier wrote:
> 
>>> +	All system register encodings above use the form
>>> +
>>> +	Op0, Op1, CRn, CRm, Op2.
>>> +
>>> +	Note that some of the encodings listed above include
>>> +	the system register space reserved for the following
>>> +	identification registers which may appear in future revisions
>>> +	of the ARM architecture beyond ARMv8.0.
>>> +	This space includes:
>>> +	ID_AA64PFR[2-7]_EL1
>>> +	ID_AA64DFR[2-3]_EL1
>>> +	ID_AA64AFR[2-3]_EL1
>>> +	ID_AA64ISAR[2-7]_EL1
>>> +	ID_AA64MMFR[2-7]_EL1
> 
> 
> AFAIK, the id space is unassigned. So the naming above could cause confusion
> if the register is named something else.

It is reserved *at the moment*, but already has a defined behaviour. My
worry is that when some new architecture revision comes around, we start
using these registers without thinking much about it (because we should
be able to). At this point, your SoC will catch fire and nobody will
have a clue about the problem because it is not apparent in the code.

I'd really like to see something a bit more forward looking that covers
that space for good.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...