Re: [PATCH V4 19/23] RISC-V: Add ACPI initialization in setup_arch()

From: Sunil V L <sunilvl@ventanamicro.com>
To: Conor Dooley <conor@kernel.org>
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-acpi@vger.kernel.org,
	linux-crypto@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, llvm@lists.linux.dev,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Tom Rix <trix@redhat.com>,
	Conor Dooley <conor.dooley@microchip.com>,
	Weili Qian <qianweili@huawei.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Jonathan Corbet <corbet@lwn.net>, Marc Zyngier <maz@kernel.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Andrew Jones <ajones@ventanamicro.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Mark Gross <markgross@kernel.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Zhou Wang <wangzhou1@hisilicon.com>,
	Palmer Dabbelt <palmer@dabbelt.com>, Len Brown <lenb@kernel.org>,
	Maximilian Luz <luzmaximilian@gmail.com>,
	"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH V4 19/23] RISC-V: Add ACPI initialization in setup_arch()
Date: Wed, 5 Apr 2023 20:41:54 +0530	[thread overview]
Message-ID: <ZC2PuiY5Xscz305H@sunil-laptop> (raw)
In-Reply-To: <20230404-escalator-fridge-daf9aaffad12@spud>

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@ventanamicro.com>
> > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> > Acked-by: Conor Dooley <conor.dooley@microchip.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(). So, parse_dtb()
would have set initial_boot_params to early VA and if we don't call
early_init_dt_verify() again with __va, it panics since
initial_boot_params can not be translated.

Thanks,
Sunil