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[222.155.5.102]) by smtp.gmail.com with ESMTPSA id k9sm13406563pgr.47.2021.12.28.20.15.25 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Dec 2021 20:15:49 -0800 (PST) Subject: Re: [RFC 02/32] Kconfig: introduce HAS_IOPORT option and select it as necessary To: Arnd Bergmann References: <20211227164317.4146918-1-schnelle@linux.ibm.com> <20211227164317.4146918-3-schnelle@linux.ibm.com> Cc: Geert Uytterhoeven , Niklas Schnelle , Bjorn Helgaas , John Garry , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Guo Ren , Dinh Nguyen , Chris Zankel , Karol Gugala , Jeff Dike , Yoshinori Sato , Brian Cain , Heiko Carstens , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Catalin Marinas , Will Deacon , Michal Simek , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Rich Felker , "David S. Miller" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-pci@vger.kernel.org, linux-riscv@lists.infradead.org, linux-csky@vger.kernel.org, linux-xtensa@linux-xtensa.org, openrisc@lists.librecores.org, linux-s390@vger.kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Greg Ungerer From: Michael Schmitz Message-ID: <1f90f145-219e-1cad-6162-9959d43a27ad@gmail.com> Date: Wed, 29 Dec 2021 17:15:23 +1300 User-Agent: Mozilla/5.0 (X11; Linux ppc; rv:45.0) Gecko/20100101 Icedove/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org Hi Arnd, Am 29.12.2021 um 16:41 schrieb Arnd Bergmann: > On Tue, Dec 28, 2021 at 8:20 PM Michael Schmitz wrote: >> Am 28.12.2021 um 23:08 schrieb Geert Uytterhoeven: >>> On Mon, Dec 27, 2021 at 5:44 PM Niklas Schnelle wrote: >>>> 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 >>>> Signed-off-by: Arnd Bergmann >>>> Signed-off-by: Niklas Schnelle >>> >>> Thanks for your patch! >>> >>>> --- a/arch/m68k/Kconfig >>>> +++ b/arch/m68k/Kconfig >>>> @@ -16,6 +16,7 @@ config M68K >>>> select GENERIC_CPU_DEVICES >>>> select GENERIC_IOMAP >>>> select GENERIC_IRQ_SHOW >>>> + select HAS_IOPORT >>>> select HAVE_AOUT if MMU >>>> select HAVE_ASM_MODVERSIONS >>>> select HAVE_DEBUG_BUGVERBOSE >>> >>> This looks way too broad to me: most m68k platform do not have I/O >>> port access support. >>> >>> My gut feeling says: >>> >>> select HAS_IOPORT if PCI || ISA >>> >>> but that might miss some intricate details... >> >> In particular, this misses the Atari ROM port ISA adapter case - >> >> select HAS_IOPORT if PCI || ISA || ATARI_ROM_ISA >> >> might do instead. > > Right, makes sense. I had suggested to go the easy way and assume that > each architecture would select HAS_IOPORT if any configuration supports > it, but it looks like for m68k there is a clearly defined set of platforms that > do. > > Note that for the platforms that don't set any of the three symbols, the > fallback makes inb() an alias for readb() with a different argument type, > so there may be m68k specific drivers that rely on this, but those would > already be broken if ATARI_ROM_ISA is set. I'd hope not - we spent some effort to make sure setting ATARI_ROM_ISA does not affect other m68k platforms when e.g. building multiplatform kernels. Replacing inb() by readb() without any address translation won't do much good for m68k though - addresses in the traditional ISA I/O port range would hit the (unmapped) zero page. Cheers, Michael > > Arnd >