linux-kernel - Re: [PATCH v3 2/2] riscv: T-Head: Test availability bit before enabling MAE errata

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Date: Mon, 8 Apr 2024 10:06:55 +0100
From: Conor Dooley <conor@...nel.org>
To: Yangyu Chen <cyy@...self.name>
Cc: Christoph Müllner <christoph.muellner@...ll.eu>,
	ajones@...tanamicro.com, alex@...ti.fr, alistair.francis@....com,
	Albert Ou <aou@...s.berkeley.edu>, bjorn@...nel.org,
	Conor Dooley <conor.dooley@...rochip.com>,
	cooper.qu@...ux.alibaba.com, dbarboza@...tanamicro.com,
	Qingfang Deng <dqfext@...il.com>, eric.huang@...ux.alibaba.com,
	heiko@...ech.de, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>, philipp.tomsich@...ll.eu,
	samuel.holland@...ive.com, zhiwei_liu@...ux.alibaba.com,
	Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v3 2/2] riscv: T-Head: Test availability bit before
 enabling MAE errata

On Mon, Apr 08, 2024 at 04:21:24PM +0800, Yangyu Chen wrote:
> 
> So the solution might be to have some property like `xtheadmae` and test
> th.sxstatus whether it has MAEE bit set when we have this in ISA string in
> the DT rather than have MAE enabled for sure if `xtheadmae` exists as
> discussed before. This will require changing the DT.

Yeah, I think I don't mind what you propose, as long as we define in the
binding that "xtheadmae" means the hardware supports it ***AND*** the bit
in the CSR. That's easier on firmware and taps into the existing
support in the kernel. I think it's more consistent with how we handle
the standard extensions to do it that way than to assume "xtheadmae"
being present means that it is enabled.

> However, since the
> C908, the first core released by T-Head that supports MAE with non-zero
> arch_id and imp_id hasn't merged to mainline yet. It's time to add this
> dt-binding and some code to probe it. I can have it tested on K230
> recently. Whatever, this patch can go first.

I don't think adding something like this should block merging the
initial c908 support though, can easily be follow-up work. I'll apply
the k230 stuff Wednesday if nothing has come in on it by then.

Cheers,
Conor.

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