linux-kernel - [PATCH] um: stop using PCI port I/O

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Message-Id: <20250509084125.1488601-1-arnd@kernel.org>
Date: Fri,  9 May 2025 10:40:52 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Richard Weinberger <richard@....at>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>
Cc: Arnd Bergmann <arnd@...db.de>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Benjamin Berg <benjamin.berg@...el.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	David Gow <davidgow@...gle.com>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	linux-um@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] um: stop using PCI port I/O

From: Arnd Bergmann <arnd@...db.de>

arch/um is one of the last users of CONFIG_GENERIC_IOMAP, but upon
closer look it appears that the PCI host bridge does not register
any port I/O, and the absense of both custom inb/outb functions and
a PCI_IOBASE constant means that actually trying to use port I/O
results on a NULL pointer access.

Build testing with clang confirms this by warning about this exact
problem:

include/asm-generic/io.h:549:31: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]
  549 |         val = __raw_readb(PCI_IOBASE + addr);
      |                           ~~~~~~~~~~ ^

Remove all the Kconfig selects that refer to legacy port I/O
and instead just build the normal MMIO path that is emulated
by the virtio PCI host.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/um/Kconfig         |  6 ------
 arch/um/kernel/Makefile |  1 -
 arch/um/kernel/ioport.c | 13 -------------
 3 files changed, 20 deletions(-)
 delete mode 100644 arch/um/kernel/ioport.c

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 79509c7f39de..f08e8a7fac93 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -52,13 +52,7 @@ config NO_IOMEM
 config UML_IOMEM_EMULATION
 	bool
 	select INDIRECT_IOMEM
-	select HAS_IOPORT
 	select GENERIC_PCI_IOMAP
-	select GENERIC_IOMAP
-	select NO_GENERIC_PCI_IOPORT_MAP
-
-config NO_IOPORT_MAP
-	def_bool !UML_IOMEM_EMULATION
 
 config ISA
 	bool
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index 4df1cd0d2017..4669db2aa9be 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -25,7 +25,6 @@ obj-$(CONFIG_GPROF)	+= gprof_syms.o
 obj-$(CONFIG_OF) += dtb.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
-obj-$(CONFIG_GENERIC_PCI_IOMAP) += ioport.o
 
 USER_OBJS := config.o
 
diff --git a/arch/um/kernel/ioport.c b/arch/um/kernel/ioport.c
deleted file mode 100644
index 7220615b3beb..000000000000
--- a/arch/um/kernel/ioport.c
+++ /dev/null
@@ -1,13 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Copyright (C) 2021 Intel Corporation
- * Author: Johannes Berg <johannes@...solutions.net>
- */
-#include <asm/iomap.h>
-#include <asm-generic/pci_iomap.h>
-
-void __iomem *__pci_ioport_map(struct pci_dev *dev, unsigned long port,
-			       unsigned int nr)
-{
-	return NULL;
-}
-- 
2.39.5