From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@arndb.de>, "H. Peter Anvin" <hpa@zytor.com>,
Niklas Schnelle <schnelle@linux.ibm.com>,
Richard Henderson <richard.henderson@linaro.org>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Matt Turner <mattst88@gmail.com>,
Russell King <linux@armlinux.org.uk>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Michal Simek <monstr@monstr.eu>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
"James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>,
Helge Deller <deller@gmx.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
Christophe Leroy <christophe.leroy@cs>
Cc: "linux-m68k@vger.kernel.org" <linux-m68k@vger.kernel.org>,
"linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
"Rafael J . Wysocki" <rafael@kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
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<linux-riscv@lists.infradead.org>,
Linux-Arch <linux-arch@vger.kernel.org>,
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"Alan Stern" <stern@rowland.harvard.edu>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"loongarch@lists.linux.dev" <loongarch@lists.linux.dev>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
linux-arm-kernel@lists.i
Subject: RE: [PATCH v4] Kconfig: introduce HAS_IOPORT option and select it as necessary
Date: Wed, 5 Apr 2023 21:36:44 +0000 [thread overview]
Message-ID: <ccff565cde1440b8bff92d96f94a32b5@AcuMS.aculab.com> (raw)
In-Reply-To: <d8686aaf-f12e-446b-9a80-335bb4266a4d@app.fastmail.com>
From: Linuxppc-dev Arnd Bergmann
> Sent: 05 April 2023 21:32
>
> On Wed, Apr 5, 2023, at 22:00, H. Peter Anvin wrote:
> > On April 5, 2023 8:12:38 AM PDT, Niklas Schnelle <schnelle@linux.ibm.com> wrote:
> >>On Thu, 2023-03-23 at 17:33 +0100, Niklas Schnelle wrote:
> >>> We introduce a new HAS_IOPORT Kconfig option to indicate 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 such as s390.
> >>> >>
> >>Gentle ping. As far as I can tell this hasn't been picked to any tree
> >>sp far but also hasn't seen complains so I'm wondering if I should send
> >>a new version of the combined series of this patch plus the added
> >>HAS_IOPORT dependencies per subsystem or wait until this is picked up.
> >
> > You need this on a system supporting not just ISA but also PCI.
> >
> > Typically on non-x86 architectures this is simply mapped into a memory window.
>
> I'm pretty confident that the list is correct here, as the HAS_IOPORT
> symbol is enabled exactly for the architectures that have a way to
> map the I/O space. PCIe generally works fine without I/O space, the
> only exception are drivers for devices that were around as early PCI.
Isn't there a difference between cpu that have inb()/outb() (probably
only x86?) and architectures (well computer designs) that can generate
PCI 'I/O' cycles by some means.
It isn't even just PCI I/O cycles, I've used an ARM cpu (SA1100)
that mapped a chuck of physical address space onto PCMCIA I/O cycles.
If the hardware can map a PCI 'IO' bar into normal kernel address
space then the bar and accesses can be treated exactly like a memory bar.
This probably leaves x86 as the outlier where you need (IIRC) io_readl()
and friends that can generate in/out instructions for those accesses.
There are also all the x86 ISA devices which need in/out instructions.
But (with the likely exception of the UART) they are pretty much
platform specific.
So, to my mind at least, HAS_IOPORT is just the wrong question.
David
next prev parent reply other threads:[~2023-04-05 21:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-23 16:33 [PATCH v4] Kconfig: introduce HAS_IOPORT option and select it as necessary Niklas Schnelle
2023-04-05 15:12 ` Niklas Schnelle
2023-04-05 20:00 ` H. Peter Anvin
2023-04-05 20:31 ` Arnd Bergmann
2023-04-05 21:36 ` David Laight [this message]
2023-04-11 8:49 ` Geert Uytterhoeven
2023-04-11 9:49 ` David Laight
2023-04-05 20:24 ` Arnd Bergmann
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