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

From: Conor Dooley <conor.dooley@microchip.com>
To: "Christoph Müllner" <christoph.muellner@vrull.eu>
Cc: "Andrew Jones" <ajones@ventanamicro.com>,
	"Conor Dooley" <conor@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Philipp Tomsich" <philipp.tomsich@vrull.eu>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Daniel Henrique Barboza" <dbarboza@ventanamicro.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Cooper Qu" <cooper.qu@linux.alibaba.com>,
	"Zhiwei Liu" <zhiwei_liu@linux.alibaba.com>,
	"Huang Tao" <eric.huang@linux.alibaba.com>,
	"Alistair Francis" <alistair.francis@wdc.com>
Subject: Re: [PATCH 2/2] riscv: T-Head: Test availability bit before enabling MAEE errata
Date: Thu, 28 Mar 2024 14:57:54 +0000	[thread overview]
Message-ID: <20240328-issuing-crouton-3448aba81b64@wendy> (raw)
In-Reply-To: <CAEg0e7jyGZV3+04HNYzgfHMGYT9wV_c0A=ekpCRi3L-5yjxK=w@mail.gmail.com>

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On Thu, Mar 28, 2024 at 03:18:22PM +0100, Christoph Müllner wrote:

> Switching from th.mxstatus to th.sxstatus should address all mentioned concerns:
> * no dependency on OpenSBI changes
> * no break of functionality
> * no need for graceful handling of CSR read failures
> * no need to differentiate between HW and emulation (assuming QEMU
> accepts the emulation of th.sxstatus)

Yah, th.sxstatus seems ideal here, provided it is accepted by QEMU - but
if they allow th.mxstatus I would hope emulating th.sxstatus would be
okay too.

> Also note that DT handling would be difficult, because we need to probe before
> setting up the page table.

IIRC the kaslr seed is also read from DT prior to calling the early
alternatives stuff, so while it would be a bit more annoying than usual
I do think it is possible. My (naive) hope here though is that we don't
actually have to deal with this scenario though, as things like the c908
support Svpbmt as well as the maee version. For the k230 the plan is
to use both Zicbom and Svpbmt rather than the non-standard T-Head
alternatives:
https://lore.kernel.org/all/tencent_DF5D7CD182AFDA188E0FB80E314A21038D08@qq.com/

Cheers,
Conor.

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