linux-kernel - Re: [PATCH] fix RTC_CLASS regression with PARISC

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Date:	Mon, 08 Sep 2008 15:28:09 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Parisc List <linux-parisc@...r.kernel.org>
Subject: Re: [PATCH] fix RTC_CLASS regression with PARISC

On Mon, 2008-09-08 at 12:13 -0700, David Brownell wrote:
> On Monday 08 September 2008, James Bottomley wrote:
> > On Mon, 2008-09-08 at 11:19 -0700, David Brownell wrote:
> > > On Monday 08 September 2008, James Bottomley wrote:
> > > > Put it back again by making RTC_CLASS 
> > > > unselectable if the architecture is parisc.
> > > 
> > > Easier if those distros just wouldn't select RTC_CLASS then.  :)
> > 
> > Yes, but think of distro config people rather like users ... if you can
> > prevent them from doing something stupid, it's a good idea.  In this
> > case, there's currently no way anyone should ever select RTC_CLASS on
> > parisc, so we should make that clear in the Kconfig file.
> 
> Preventing them from doing stupid stuff is exactly why we
> have Kconfig prevent both legacy *AND* framework RTC code
> from being selected.  :)
> 
> Of course stupidity is infinite, and we didn't know about
> this particular instance in advance...
> 
> 
> > > And long term, better to work with RTC_CLASS.  Eliminate that
> > > crufty asm-parisc/rtc.h file and one more GEN_RTC user; and
> > > share more widely-used infrastructure.
> > > 
> > > If I read things right, that would be easy:  the PARISC RTC is
> > > two firmware calls, ptc_tod_{read,set}(), which would map to
> > > RTC class {read,set}_time() methods of about six lines each.
> > > The RTC framework can do UIE emulation, if needed.
> > 
> > OK, I can look at that, but in the mean time could we make the option
> > that causes the damage unselectable?
> 
> I'd worry if "the mean time" takes too long.  But lacking a
> PARISC laptop to fix this on, I'm unlikely to complain much.

What is the expectation?  If you're expecting all the architectures to
migrate over to RTC_CLASS, actually telling linux-arch and saying why
its a good idea would have been helpful.

All the PDC real time clock calls can do are read and set, nothing else,
so it's idealy suited to the GEN_RTC infrastructure ... what's the
benefit in moving it to RTC_CLASS?

> >	 This is technically a regression 
> > because before your patch GEN_RTC would override RTC_CLASS, now it's the
> > other way around.
> 
> Well, previously there was no override ... I think you mean
> that parisc just completely ignored RTC_CLASS, treating it
> like junk DNA.

No, it's a regression.  You made it so when you added this

#
# These legacy RTC drivers just cause too many conflicts with the
generic
# RTC framework ... let's not even try to coexist any more.
#
if RTC_LIB=n

Around the GEN_RTC configuration.  This turns off the ability to select
GEN_RTC if you've said yes to RTC_CLASS.  Since RTC_CLASS is currently
unsupported on parisc, we need to fix that by making the RTC_CLASS
option unselectable on parisc.

James


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