Date: Tue, 23 Jan 2024 15:05:53 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Philipp Stanner <pstanner@...hat.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Johannes Berg <johannes@...solutions.net>,
	Randy Dunlap <rdunlap@...radead.org>, NeilBrown <neilb@...e.de>,
	John Sanpe <sanpeqf@...il.com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Uladzislau Koshchanka <koshchanka@...il.com>,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	David Gow <davidgow@...gle.com>, Kees Cook <keescook@...omium.org>,
	Rae Moar <rmoar@...gle.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"wuqiang.matt" <wuqiang.matt@...edance.com>,
	Yury Norov <yury.norov@...il.com>, Jason Baron <jbaron@...mai.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marco Elver <elver@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ben Dooks <ben.dooks@...ethink.co.uk>, dakr@...hat.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arch@...r.kernel.org, stable@...r.kernel.org,
	Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH v5 RESEND 5/5] lib, pci: unify generic pci_iounmap()

On Thu, Jan 11, 2024 at 09:55:40AM +0100, Philipp Stanner wrote:
> The implementation of pci_iounmap() is currently scattered over two
> files, drivers/pci/iomap.c and lib/iomap.c. Additionally,
> architectures can define their own version.
> 
> To have only one version, it's necessary to create a helper function,
> iomem_is_ioport(), that tells pci_iounmap() whether the passed address
> points to an ioport or normal memory.
> 
> iomem_is_ioport() can be provided through two different ways:
>   1. The architecture itself provides it. As of today, the version
>      coming from lib/iomap.c de facto is the x86-specific version and
>      comes into play when CONFIG_GENERIC_IOMAP is selected. This rather
>      confusing naming is an artifact left by the removal of IA64.
>   2. As a default version in include/asm-generic/io.h for those
>      architectures that don't use CONFIG_GENERIC_IOMAP, but also don't
>      provide their own version of iomem_is_ioport().
> 
> Once all architectures that support ports provide iomem_is_ioport(), the
> arch-specific definitions for pci_iounmap() can be removed and the archs
> can use the generic implementation, instead.
> 
> Create a unified version of pci_iounmap() in drivers/pci/iomap.c.
> Provide the function iomem_is_ioport() in include/asm-generic/io.h
> (generic) and lib/iomap.c ("pseudo-generic" for x86).
> 
> Remove the CONFIG_GENERIC_IOMAP guard around
> ARCH_WANTS_GENERIC_PCI_IOUNMAP so that configs that set
> CONFIG_GENERIC_PCI_IOMAP without CONFIG_GENERIC_IOMAP still get the
> function.
> 
> Add TODOs for follow-up work on the "generic is not generic but
> x86-specific"-Problem.
> ...

> +++ b/drivers/pci/iomap.c
> @@ -135,44 +135,30 @@ void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long maxlen)
>  EXPORT_SYMBOL_GPL(pci_iomap_wc);
>  
>  /*
> - * pci_iounmap() somewhat illogically comes from lib/iomap.c for the
> - * CONFIG_GENERIC_IOMAP case, because that's the code that knows about
> - * the different IOMAP ranges.
> + * This check is still necessary due to legacy reasons.
>   *
> - * But if the architecture does not use the generic iomap code, and if
> - * it has _not_ defined it's own private pci_iounmap function, we define
> - * it here.
> - *
> - * NOTE! This default implementation assumes that if the architecture
> - * support ioport mapping (HAS_IOPORT_MAP), the ioport mapping will
> - * be fixed to the range [ PCI_IOBASE, PCI_IOBASE+IO_SPACE_LIMIT [,
> - * and does not need unmapping with 'ioport_unmap()'.
> - *
> - * If you have different rules for your architecture, you need to
> - * implement your own pci_iounmap() that knows the rules for where
> - * and how IO vs MEM get mapped.
> - *
> - * This code is odd, and the ARCH_HAS/ARCH_WANTS #define logic comes
> - * from legacy <asm-generic/io.h> header file behavior. In particular,
> - * it would seem to make sense to do the iounmap(p) for the non-IO-space
> - * case here regardless, but that's not what the old header file code
> - * did. Probably incorrectly, but this is meant to be bug-for-bug
> - * compatible.

Moving this comment update to the patch that adds the ioport_unmap()
call would make that patch more consistent and simplify this patch.

> + * TODO: Have all architectures that provide their own pci_iounmap() provide
> + * iomem_is_ioport() instead. Remove this #if afterwards.
>   */
>  #if defined(ARCH_WANTS_GENERIC_PCI_IOUNMAP)
>  
> -void pci_iounmap(struct pci_dev *dev, void __iomem *p)
> +/**
> + * pci_iounmap - Unmapp a mapping
> + * @dev: PCI device the mapping belongs to
> + * @addr: start address of the mapping
> + *
> + * Unmapp a PIO or MMIO mapping.

s/Unmapp/Unmap/ (twice)

> + */
> +void pci_iounmap(struct pci_dev *dev, void __iomem *addr)

Maybe move the "p" to "addr" rename to the patch that fixes the
pci_iounmap() #ifdef problem, since that's a trivial change that
already has to do with handling both PIO and MMIO?  Then this patch
would be a little more focused.

The kernel-doc addition could possibly also move there since it isn't
related to the unification.

>  {
> -#ifdef ARCH_HAS_GENERIC_IOPORT_MAP
> -	uintptr_t start = (uintptr_t) PCI_IOBASE;
> -	uintptr_t addr = (uintptr_t) p;
> -
> -	if (addr >= start && addr < start + IO_SPACE_LIMIT) {
> -		ioport_unmap(p);
> +#ifdef CONFIG_HAS_IOPORT_MAP
> +	if (iomem_is_ioport(addr)) {
> +		ioport_unmap(addr);
>  		return;
>  	}
>  #endif
> -	iounmap(p);
> +
> +	iounmap(addr);
>  }

> + * If CONFIG_GENERIC_IOMAP is selected and the architecture does NOT provide its
> + * own version, ARCH_WANTS_GENERIC_IOMEM_IS_IOPORT makes sure that the generic
> + * version from asm-generic/io.h is NOT used and instead the second "generic"
> + * version from this file here is used.
> + *
> + * There are currently two generic versions because of a difficult cleanup
> + * process. Namely, the version in lib/iomap.c once was really generic when IA64
> + * still existed. Today, it's only really used by x86.
> + *
> + * TODO: Move this function to x86-specific code.

Some of these TODOs look fairly simple.  Are they actually hard, or
could they just be done now?

It seems like implementing iomem_is_ioport() for the other arches
would be straightforward and if done first, could make this patch look
tidier.

Or if the TODOs can't be done now, maybe the iomem_is_ioport()
addition could be done as a separate patch to make the unification
more obvious.

> + */
> +#if defined(ARCH_WANTS_GENERIC_IOMEM_IS_IOPORT)
> +bool iomem_is_ioport(void __iomem *addr)
>  {
> -	IO_COND(addr, /* nothing */, iounmap(addr));
> +	unsigned long port = (unsigned long __force)addr;
> +
> +	if (port > PIO_OFFSET && port < PIO_RESERVED)
> +		return true;
> +
> +	return false;
>  }
> -EXPORT_SYMBOL(pci_iounmap);
> -#endif /* CONFIG_PCI */
> +#endif /* ARCH_WANTS_GENERIC_IOMEM_IS_IOPORT */
> -- 
> 2.43.0
> 

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