Re: [PATCH v3 28/38] rtc: add HAS_IOPORT dependencies

From: "Arnd Bergmann" <arnd@arndb.de>
To: "Niklas Schnelle" <schnelle@linux.ibm.com>,
	"Alexandre Belloni" <alexandre.belloni@bootlin.com>
Cc: "Alessandro Zummo" <a.zummo@towertech.it>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	linux-kernel@vger.kernel.org,
	Linux-Arch <linux-arch@vger.kernel.org>,
	linux-pci@vger.kernel.org, "Arnd Bergmann" <arnd@kernel.org>,
	linux-rtc@vger.kernel.org
Subject: Re: [PATCH v3 28/38] rtc: add HAS_IOPORT dependencies
Date: Mon, 08 May 2023 22:01:08 +0200	[thread overview]
Message-ID: <b7017996-b079-4534-a24a-080003772a66@app.fastmail.com> (raw)
In-Reply-To: <aa68b4afdca34bf3bfd2439b03e6f9bcfad94903.camel@linux.ibm.com>

On Mon, May 8, 2023, at 17:36, Niklas Schnelle wrote:
> On Tue, 2023-03-14 at 13:52 +0100, Alexandre Belloni wrote:
>> Hello,
>> 
>> On 14/03/2023 13:12:06+0100, Niklas Schnelle wrote:
>> > In a future patch HAS_IOPORT=n will result in inb()/outb() and friends
>> > not being declared. We thus need to add HAS_IOPORT as dependency for
>> > those drivers using them.
>> > 
>> > Co-developed-by: Arnd Bergmann <arnd@kernel.org>
>> > Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
>> > ---
>> >  drivers/rtc/Kconfig | 4 +++-
>> >  1 file changed, 3 insertions(+), 1 deletion(-)
>> > 
>> > diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
>> > index 5a71579af0a1..20aa77bf0a9f 100644
>> > --- a/drivers/rtc/Kconfig
>> > +++ b/drivers/rtc/Kconfig
>> > @@ -956,6 +956,7 @@ comment "Platform RTC drivers"
>> >  config RTC_DRV_CMOS
>> >  	tristate "PC-style 'CMOS'"
>> >  	depends on X86 || ARM || PPC || MIPS || SPARC64
>> > +	depends on HAS_IOPORT
>> 
>> Did you check that this will not break platforms that doesn't have RTC_PORT defined?
>> > 
>
> From what I can tell the CMOS_READ() macro this driver relies on uses
> some form of inb() style I/O port access in all its definitions. So my
> understanding is that this device is always accessed via I/O ports even
> if the variants differ slightly and would make no sense on a platform
> without any way of accessing I/O ports which is what lack of HAS_IOPORT
> means. From what I can see even without RTC_PORT being defined the
> CMOS_READ is still used. Hope that answers your question?

I think the m68k/atari and mips/dec variants don't necessarily
qualify as PIO, those are really just pointer dereferences, and
they don't use the actual inb/outb functions.

On atari, it looks like HAS_IOPORT may be set if ATARI_ROM_ISA
is, but on dec it's never enabled.

    Arnd