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Date:   Sun, 25 Jun 2023 15:36:06 -0700 (PDT)
Subject:     Re: [PATCH V1 1/3] Revert "RISC-V: mark hibernation as nonportable"
In-Reply-To: <20230625-obstinate-grimy-b765a1d3d741@spud>
CC:     suagrfillet@gmail.com, Paul Walmsley <paul.walmsley@sifive.com>,
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        mpe@ellerman.id.au, Arnd Bergmann <arnd@arndb.de>, rppt@kernel.org,
        samuel@sholland.org, panqinglin2020@iscas.ac.cn,
        Conor Dooley <conor.dooley@microchip.com>, anup@brainfault.org,
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From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     Conor Dooley <conor@kernel.org>
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On Sun, 25 Jun 2023 15:15:14 PDT (-0700), Conor Dooley wrote:
> 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.
>> 
>> 在 2023/6/25 22:18, Conor Dooley 写道:
>> > On Sun, Jun 25, 2023 at 10:09:29PM +0800, Song Shuai wrote:
>> > > This reverts commit ed309ce522185583b163bd0c74f0d9f299fe1826.
>> > > 
>> > > 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.
>> > 
>> > > And firmware always
>> > > correctly mark resident memory, or memory protected with PMP as
>> > > per the devicetree specification and/or the UEFI specification.
>> > 
>> > But this is not true? The versions of OpenSBI that you mention in your
>> > cover letter do not do this.
>> > Please explain.
>> > 
>> 
>> At this time, OpenSbi [v0.8,v1.3) and edk2(RiscVVirt) indeed don't obey the
>> DT/UEFI spec. This statement is excerpted from "Reserved memory for resident
>> firmware" part from the upcoming riscv/boot.rst. It isn't accurate for now.
>> 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.

Is there any actual use case for hibernation on these boards?  Maybe 
it's simpler to just add a "reserved regions actually work" sort of 
property and then have new firmware set it -- that way we can avoid 
sorting through all the old stuff nobody cares about and just get on 
with fixing the stuff people use.

>
> Cheers,
> Conor.
>
>> > > So those regions will not be mapped in the linear mapping and they
>> > > can be safely saved/restored by hibernation.
>> > > 
>> > > Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
>> > > ---
>> > >   arch/riscv/Kconfig | 5 +----
>> > >   1 file changed, 1 insertion(+), 4 deletions(-)
>> > > 
>> > > 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 implementation 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
>> > > -- 
>> > > 2.20.1
>>