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Date: Fri, 5 Apr 2024 16:52:27 +0100
From: Conor Dooley <conor@kernel.org>
To: Yangyu Chen <cyy@cyyself.name>
Cc: Icenowy Zheng <uwu@icenowy.me>, linux-riscv@lists.infradead.org,
	Damien Le Moal <dlemoal@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Philipp Zabel <p.zabel@pengutronix.de>, linux-gpio@vger.kernel.org,
	linux-clk@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 10/11] riscv: dts: add initial canmv-k230 and k230-evb
 dts
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On Mon, Mar 25, 2024 at 11:10:49AM +0800, Yangyu Chen wrote:
> > On Mar 25, 2024, at 00:23, Icenowy Zheng <uwu@icenowy.me> wrote:
> > =E5=9C=A8 2024-03-23=E6=98=9F=E6=9C=9F=E5=85=AD=E7=9A=84 20:12 +0800=EF=
=BC=8CYangyu Chen=E5=86=99=E9=81=93=EF=BC=9A
> >> - Svpbmt and T-Head MAEE both supported
> >>=20
> >> T-Head C908 does support both Svpbmt and T-Head MAEE for page-based
> >> memory
> >> attributes and is controlled by BIT(21) on CSR.MXSTATUS. The Svpbmt
> >> is used
> >> here for mainline kernel support for K230. If the kernel wants to use
> >> Svpbmt, the M-Mode software should unset BIT(21) of CSR.MXSTATUS
> >> before
> >> entering the S-Mode kernel. Otherwise, the kernel will not boot, as 0
> >> on
> >> T-Head MAEE is NonCachable Memory. Once the kernel switches from bare
> >> metal
> >> to Sv39, It will lose dirty cache line modifications that haven't
> >> been
> >> written back to the memory.
> >=20
> > As MXSTATUS has a S-mode read-only mirror known as SXSTATUS, maybe the
> > kernel should detect SXSTATUS to decide whether to use Svpbmt or
> > Xtheadpbmt (BTW Svnapot conflicts with Xtheadpbmt too).
> >=20
>=20
> Thanks for this hint. I may need to change some code in the T-Head PBMT p=
robe.

For now, I'd rather we just focused on supporting the standard
extensions on this SoC in mainline. I've applied the patches re-doing
the Kconfig options just now, feel free to resend these patches
whenever.

Thanks,
Conor.

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