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Date:   Sun, 25 Jun 2023 23:15:14 +0100
From:   Conor Dooley <conor@kernel.org>
To:     Song Shuai <suagrfillet@gmail.com>
Cc:     paul.walmsley@sifive.com, palmer@dabbelt.com,
        aou@eecs.berkeley.edu, robh+dt@kernel.org, frowand.list@gmail.com,
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        conor.dooley@microchip.com, anup@brainfault.org,
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        heiko@sntech.de, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH V1 1/3] Revert "RISC-V: mark hibernation as nonportable"
Message-ID: <20230625-obstinate-grimy-b765a1d3d741@spud>
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Hey,

On Sun, Jun 25, 2023 at 11:09:21PM +0800, Song Shuai wrote:

> Sorry for the delayed reply,

It wasn't really delayed at all actually, you replied within an hour or
so, AFAICT.

> My tinylab email went something wrong, I'll use gmail in this thread.
>=20
> =E5=9C=A8 2023/6/25 22:18, Conor Dooley =E5=86=99=E9=81=93:
> > On Sun, Jun 25, 2023 at 10:09:29PM +0800, Song Shuai wrote:
> > > This reverts commit ed309ce522185583b163bd0c74f0d9f299fe1826.
> > >=20
> > > With the commit 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the
> > > linear mapping") reverted, the MIN_MEMBLOCK_ADDR points the kernel
> > > load address which was placed at a PMD boundary.
> >=20
> > > And firmware always
> > > correctly mark resident memory, or memory protected with PMP as
> > > per the devicetree specification and/or the UEFI specification.
> >=20
> > But this is not true? The versions of OpenSBI that you mention in your
> > cover letter do not do this.
> > Please explain.
> >=20
>=20
> At this time, OpenSbi [v0.8,v1.3) and edk2(RiscVVirt) indeed don't obey t=
he
> DT/UEFI spec. This statement is excerpted from "Reserved memory for resid=
ent
> firmware" part from the upcoming riscv/boot.rst. It isn't accurate for no=
w.
> How about deleting this one?

It is incorrect, so it will need to be removed, yes.
Unfortunately writing a doc does not fix the existing implementations :(

> Actually with 3335068f8721 reverted, the change of MIN_MEMBLOCK_ADDR can
> avoid the mapping of firmware memory, I will make it clear in the next
> version.

To be honest, I'd like to see this revert as the final commit in a
series that deals with the problem by actually reserving the regions,
rather than a set of reverts that go back to how we were.
I was hoping that someone who cares about hibernation support would be
interested in working on that - *cough* starfive *cough*, although maybe
they just fixed their OpenSBI and moved on.
If there were no volunteers, my intention was to add a firmware erratum
that would probe the SBI implementation & version IDs, and add a firmware
erratum that'd parse the DT for the offending regions and reserve them.

Cheers,
Conor.

> > > So those regions will not be mapped in the linear mapping and they
> > > can be safely saved/restored by hibernation.
> > >=20
> > > Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
> > > ---
> > >   arch/riscv/Kconfig | 5 +----
> > >   1 file changed, 1 insertion(+), 4 deletions(-)
> > >=20
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index 5966ad97c30c..17b5fc7f54d4 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -800,11 +800,8 @@ menu "Power management options"
> > >   source "kernel/power/Kconfig"
> > > -# Hibernation is only possible on systems where the SBI implementati=
on has
> > > -# marked its reserved memory as not accessible from, or does not run
> > > -# from the same memory as, Linux
> > >   config ARCH_HIBERNATION_POSSIBLE
> > > -	def_bool NONPORTABLE
> > > +	def_bool y
> > >   config ARCH_HIBERNATION_HEADER
> > >   	def_bool HIBERNATION
> > > --=20
> > > 2.20.1
>

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