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

[Sunil V L <sunilvl@ventanamicro.com>]

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