linux-kernel - Re: [rtc-linux] Re: [PATCH/RFC 0/5] Generic RTC class driver

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Message-ID: <alpine.LRH.2.00.0903021116450.25117@vixen.sonytel.be>
Date:	Mon, 2 Mar 2009 11:28:01 +0100 (CET)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Alessandro Zummo <alessandro.zummo@...ertech.it>
cc:	Richard Zidlicky <rz@...ux-m68k.org>, rtc-linux@...glegroups.com,
	David Woodhouse <dwmw2@...radead.org>,
	linux-parisc@...r.kernel.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	David@...abs.org, Kyle McMartin <kyle@...artin.ca>,
	Linux/PPC Development <linuxppc-dev@...abs.org>,
	Linux/m68k <linux-m68k@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [rtc-linux] Re: [PATCH/RFC 0/5] Generic RTC class driver

On Mon, 2 Mar 2009, Alessandro Zummo wrote:
> On Mon, 2 Mar 2009 10:54:14 +0100 (CET)
> Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com> wrote:
> > Indeed. You can have a working RTC class driver for lots of hardware by just
> > writing ca. 100 lines of code on top of the generic framework.
> 
>  That's true, but we would then have two generic frameworks. And one
>  of them will have its code scattered all around the kernel.
> 
>  So you either use the old rtc framework, which is perfectly functional,
>  or you move to the new rtc lass and write the drivers.

So I can solve my problem (autoloading the RTC driver on PS3 by udev) by
converting the old genrtc driver into a platform device driver and creating
platform devices where appropriate.

However, this doesn't solve the distro's problem: as the old RTC framework
depends on RTC_LIB=n, you cannot have both old and new RTC drivers in your
(single) distro kernel. That's why dmwm2 created drivers/rtc/rtc-ppc.c: Fedora
had to support machines with both old and new RTC drivers. As all of the old
drivers are actually behind the ppc_md.[sg]et_rtc_time() abstraction, this was
very easy.

Hence it's all or nothing, and we have to convert all of them.

drivers/rtc/rtc-generic.c would allow to have a working system without old
RTC drivers, until all low-level code has been converted to individual RTC
drivers.

>  Layering a generic framework over another generic framework
>  is quite a nonsense . 

IMHO these two generic frameworks are quite different: [sg]et_rtc_time()
abstracts the low-level RTC hardware interface, while RTC class handles the
interaction with userspace.

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
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E-mail:   Geert.Uytterhoeven@...ycom.com
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