linux-kernel - Re: [PATCH V4 19/23] RISC-V: Add ACPI initialization in setup

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Date:   Wed, 5 Apr 2023 16:30:21 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Sunil V L <sunilvl@...tanamicro.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-acpi@...r.kernel.org,
        linux-crypto@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        llvm@...ts.linux.dev,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Tom Rix <trix@...hat.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Weili Qian <qianweili@...wei.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jonathan Corbet <corbet@....net>,
        Marc Zyngier <maz@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Mark Gross <markgross@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Len Brown <lenb@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH V4 19/23] RISC-V: Add ACPI initialization in setup_arch()

On Wed, Apr 05, 2023 at 08:41:54PM +0530, Sunil V L wrote:
> On Tue, Apr 04, 2023 at 10:38:56PM +0100, Conor Dooley wrote:
> > On Tue, Apr 04, 2023 at 11:50:33PM +0530, Sunil V L wrote:
> > > Initialize the ACPI core for RISC-V during boot.
> > > 
> > > ACPI tables and interpreter are initialized based on
> > > the information passed from the firmware and the value of
> > > the kernel parameter 'acpi'.
> > > 
> > > With ACPI support added for RISC-V, the kernel parameter 'acpi'
> > > is also supported on RISC-V. Hence, update the documentation.
> > > 
> > > Signed-off-by: Sunil V L <sunilvl@...tanamicro.com>
> > > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> > > Acked-by: Conor Dooley <conor.dooley@...rochip.com>
> > 
> > > +	/* Parse the ACPI tables for possible boot-time configuration */
> > > +	acpi_boot_table_init();
> > > +	if (acpi_disabled) {
> > > +		if (IS_ENABLED(CONFIG_BUILTIN_DTB)) {
> > > +			unflatten_and_copy_device_tree();
> > > +		} else {
> > > +			if (early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa))))
> > > +				unflatten_device_tree();
> > > +			else
> > > +				pr_err("No DTB found in kernel mappings\n");
> > > +		}
> > > +	} else {
> > > +		early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa)));
> > 
> > I'm probably forgetting something, but this seems very non-obvious to
> > me:
> > Why are you running early_init_dt_verify() when ACPI is enabled?
> > I think that one deserves a comment so that next time someone looks at
> > this (that doesn't live in ACPI land) they've know exactly why this is
> > like it is.
> > 
> > Doubly so since this is likely to change with some of Alex's bits moving
> > the dtb back into the fixmap.
> > 
> Good question. The kernel creates a tiny DTB even when the FW didn't
> pass the FDT (ACPI systems). Please see update_fdt().

Can you add a comment about this either on-location or in the commit
message please?
I think this counts as non-obvious behaviour. At least to me it does!

Cheers,
Conor.


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