linux-kernel - Re: [PATCH] char: rtc: remove unused rtc

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Message-ID: <CAK8P3a0QZNY+K+V1HG056xCerz=_L2jh5UfZ+2LWkDqkw5Zznw@mail.gmail.com>
Date:   Wed, 7 Feb 2018 11:24:27 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>, linux-alpha@...r.kernel.org
Subject: Re: [PATCH] char: rtc: remove unused rtc_control() API

On Wed, Feb 7, 2018 at 2:04 AM, Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
> On 07/02/2018 at 00:24:11 +0100, Arnd Bergmann wrote:
>> On Tue, Feb 6, 2018 at 11:12 PM, Alexandre Belloni
>> <alexandre.belloni@...tlin.com> wrote:
>> > Since commit 34ce71a96dcb ("ALSA: timer: remove legacy rtctimer"), the
>> > rtc_register/rtc_control/rtc_unregister API is unused. As it is highly
>> > unlikely to be needed again, remove it.
>> >
>> > Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
>> > ---
>>
>> Nice!
>>
>> Acked-by: Arnd Bergmann <arnd@...db.de>
>>
>> I forgot what's stopping us from removing the rest of that driver ;-)
>> Since we can only build it on alpha and mips/loongson64 these
>> days, is there anything that this driver does that the normal
>> one doesn't? If it's just a question of testing, we could probably
>> just move it to staging and see if anyone notices a difference.
>
> I'd say it is a matter of testing. The loongsoon maintainers seem
> responsive so we may get testing for that architecture. I'm not so sure
> about alpha. Actually, I'm not even sure it is really used on alpha
> because arch/alpha/kernel/rtc.c seems to do the right thing.

The Alpha defconfig still enables it, and doesn't enable RTC_CLASS,
so at least that has to be changed. I've added the Alpha maintainers
to Cc, they can probably find out whether it works or not.

> I think I'll start by ripping of all the x86 and sparc specific parts
> and see what's left.

Just wait till we hear back from the others, removing it completely
would be simpler ;-)

> I would also love to get rid of drivers/char/efirtc.c but that probably
> means doing some testing on both an ARM/ARM64 platform with EFI and
> IA64.

On ARM/ARM64, we can only use the drivers/rtc/rtc-efi.c driver,
not drivers/char/efirtc.c, so it's only IA64, and they were also
the ones that sent the rtc-efi driver before the start of the git
history. However, the EFI_RTC driver is still in their defconfigs.

For the other RTC drivers in drivers/char, JS_RTC has been dead
for a while, since sparc selects RTC_CLASS. For DS1302, we
have both a driver that is used on m32r and a generic rtc class
driver for the same chip, but I wouldn't trust on that to work
on m32r. We can probably find a solution for this one once
the others are gone, e.g. removing arch/m32r, or adding some
glue logic to make it plausible for the rtc class driver to work,
without actually testing it.

     Arnd