linux-kernel - Re: [PATCH v3 28/38] rtc: add HAS

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Message-Id: <552c51fb-41b2-430b-b13c-0e578098dbf6@app.fastmail.com>
Date:   Tue, 09 May 2023 10:22:42 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Geert Uytterhoeven" <geert@...ux-m68k.org>
Cc:     "Niklas Schnelle" <schnelle@...ux.ibm.com>,
        "Alexandre Belloni" <alexandre.belloni@...tlin.com>,
        "Alessandro Zummo" <a.zummo@...ertech.it>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        "Mauro Carvalho Chehab" <mchehab@...nel.org>,
        "Alan Stern" <stern@...land.harvard.edu>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        "Palmer Dabbelt" <palmer@...belt.com>,
        "Albert Ou" <aou@...s.berkeley.edu>, linux-kernel@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-pci@...r.kernel.org, "Arnd Bergmann" <arnd@...nel.org>,
        linux-rtc@...r.kernel.org,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>
Subject: Re: [PATCH v3 28/38] rtc: add HAS_IOPORT dependencies

On Tue, May 9, 2023, at 08:38, Geert Uytterhoeven wrote:
> On Mon, May 8, 2023 at 10:01 PM Arnd Bergmann <arnd@...db.de> wrote:
>> On Mon, May 8, 2023, at 17:36, Niklas Schnelle wrote:
>>
>> 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.
>
> Atari does not use RTC_DRV_CMOS, but still relies on generic RTC
> instead.

Ah right, I now remember working on that code, so we're good on
m68k then. I think it should work for everyone using

       depends on HAS_IOPORT || ARCH_DECSTATION

in that case, as that is the only exception.

> Last time (in 2013?) I tried converting to RTC_DRV_CMOS by registering
> an "rtc_cmos" platform device, I couldn't get it to work.

If you ever want to revisit this, I suspect the harder part here
is to detach arch/m68k/ from the RTC_DRV_GENERIC code first, pushing
the device registration into the individual machine specific time.c
code. It's probably not even worth trying to share the rtc-cmos
driver, but it might be useful to share the library code like
RTC_DRV_ALPHA does.

   Arnd