linux-kernel - Re: [PATCH v2] of: OF_IRQ: select IRQ

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Date: Wed, 14 Feb 2024 18:22:53 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Marc Zyngier" <maz@...nel.org>
Cc: "Randy Dunlap" <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>, "Rob Herring" <robh@...nel.org>,
 "Philipp Zabel" <p.zabel@...gutronix.de>, "Peter Rosin" <peda@...ntia.se>,
 devicetree@...r.kernel.org
Subject: Re: [PATCH v2] of: OF_IRQ: select IRQ_DOMAIN instead of depending on it

On Wed, Feb 14, 2024, at 17:35, Marc Zyngier wrote:
> On Wed, 14 Feb 2024 16:06:06 +0000,
> "Arnd Bergmann" <arnd@...db.de> wrote:
>> 
>> On Wed, Feb 14, 2024, at 10:52, Marc Zyngier wrote:
>> > On Tue, 13 Feb 2024 22:56:19 +0000, Randy Dunlap <rdunlap@...radead.org> wrote:
>> >>
>> >> diff -- a/drivers/of/Kconfig b/drivers/of/Kconfig
>> >> --- a/drivers/of/Kconfig
>> >> +++ b/drivers/of/Kconfig
>> >> @@ -80,7 +80,8 @@ config OF_ADDRESS
>> >>  
>> >>  config OF_IRQ
>> >>  	def_bool y
>> >> -	depends on !SPARC && IRQ_DOMAIN
>> >> +	depends on !SPARC
>> >> +	select IRQ_DOMAIN
>> > 
>> >
>> > This seems to be moving is the right direction.
>> 
>> Can we move the 'select IRQ_DOMAIN' under CONFIG_IRQCHIP
>> then and remove the individual selects from the irqchip
>> drivers? It looks like CONFIG_OF (other than sparc) now
>> unconditionally enables OF_IRQ and IRQCHIP anyway.
>
> As long as it also works ACPI, it should be OK.

Out of the four architectures that have ACPI support (x86,
arm64, loongarch, rv64), only x86 doesn't always select
IRQ_DOMAIN already, and x86 selects it for almost all
configs:

config X86_UP_APIC
        bool "Local APIC support on uniprocessors" if !PCI_MSI
        default PCI_MSI
        depends on X86_32 && !SMP && !X86_32_NON_STANDARD

config X86_LOCAL_APIC
        def_bool y
        depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
        select IRQ_DOMAIN_HIERARCHY

so it's only disabled here with

CONFIG_64BIT=n
CONFIG_SMP=n
CONFIG_X86_32_NON_STANDARD=n
CONFIG_ACPI=y
CONFIG_PCI=y (implied by ACPI)
CONFIG_PCI_MSI=n

As far as I can tell, this specific configuration is
currently able to save a little bit of kernel size
by avoiding IRQ_DOMAIN, but we are probably better off
enabling it here as well for consistency

     Arnd