linux-kernel - Re: [RFC 02/32] Kconfig: introduce HAS_IOPORT option and select it as necessary

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Date:   Tue, 28 Dec 2021 17:32:02 +0100
From:   Mauro Carvalho Chehab <mchehab@...nel.org>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        John Garry <john.garry@...wei.com>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Chris Zankel <chris@...kel.net>,
        Karol Gugala <kgugala@...micro.com>,
        Jeff Dike <jdike@...toit.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Brian Cain <bcain@...eaurora.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Vineet Gupta <vgupta@...nel.org>,
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Subject: Re: [RFC 02/32] Kconfig: introduce HAS_IOPORT option and select it
 as necessary

Em Mon, 27 Dec 2021 17:42:47 +0100
Niklas Schnelle <schnelle@...ux.ibm.com> escreveu:

> We introduce a new HAS_IOPORT Kconfig option to gate support for
> I/O port access. In a future patch HAS_IOPORT=n will disable compilation
> of the I/O accessor functions inb()/outb() and friends on architectures
> which can not meaningfully support legacy I/O spaces. On these platforms
> inb()/outb() etc are currently just stubs in asm-generic/io.h which when
> called will cause a NULL pointer access which some compilers actually
> detect and warn about.
> 
> The dependencies on HAS_IOPORT in drivers as well as ifdefs for
> HAS_IOPORT specific sections will be added in subsequent patches on
> a per subsystem basis. Then a final patch will ifdef the I/O access
> functions on HAS_IOPORT thus turning any use not gated by HAS_IOPORT
> into a compile-time warning.
> 
> Link: https://lore.kernel.org/lkml/CAHk-=wg80je=K7madF4e7WrRNp37e3qh6y10Svhdc7O8SZ_-8g@mail.gmail.com/
> Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>

...

> @@ -486,6 +487,9 @@ config HAS_IOMEM
>  	depends on !NO_IOMEM
>  	default y
>  
> +config HAS_IOPORT
> +	def_bool ISA || LEGACY_PCI
> +

That doesn't sound right. 

The only dependency for LEGACY_PCI is PCI. If one selects LEGACY_PCI
on an architecture that doesn't support it, this will cause problems.

Instead, HAS_IOPORT should be selected at architecture level, and
the dependency here should be just the opposite: LEGACY_API should
depends on HAS_IOPORT.

Thanks,
Mauro