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

From: Conor Dooley <conor@kernel.org>
To: Yangyu Chen <cyy@cyyself.name>
Cc: "Christoph Müllner" <christoph.muellner@vrull.eu>,
	ajones@ventanamicro.com, alex@ghiti.fr, alistair.francis@wdc.com,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	bjorn@kernel.org, "Conor Dooley" <conor.dooley@microchip.com>,
	cooper.qu@linux.alibaba.com, dbarboza@ventanamicro.com,
	"Qingfang Deng" <dqfext@gmail.com>,
	eric.huang@linux.alibaba.com, heiko@sntech.de,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	philipp.tomsich@vrull.eu, samuel.holland@sifive.com,
	zhiwei_liu@linux.alibaba.com, "Guo Ren" <guoren@kernel.org>
Subject: Re: [PATCH v3 2/2] riscv: T-Head: Test availability bit before enabling MAE errata
Date: Mon, 8 Apr 2024 10:06:55 +0100	[thread overview]
Message-ID: <20240408-semisweet-class-39239c279adc@spud> (raw)
In-Reply-To: <tencent_D6D1043732E63644A4B1838F4210499BCF05@qq.com>

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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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