linux-kernel - Re: [PATCH v9 00/22] Re-use nvram module

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Date:   Wed, 23 Jan 2019 09:06:30 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:     Arnd Bergmann <arnd@...db.de>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Michael Schmitz <schmitzmic@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Joshua Thompson <funaho@...ai.org>,
        linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linuxppc-dev@...ts.ozlabs.org, linux-scsi@...r.kernel.org,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v9 00/22] Re-use nvram module

On Tue, 22 Jan 2019, Greg Kroah-Hartman wrote:

> On Tue, Jan 15, 2019 at 03:18:56PM +1100, Finn Thain wrote:
> > The "generic" NVRAM module, drivers/char/generic_nvram.c, implements a
> > /dev/nvram misc device. This module is used only by 32-bit PowerPC
> > platforms.
> > 
> > The RTC "CMOS" NVRAM module, drivers/char/nvram.c, also implements a
> > /dev/nvram misc device. This module is now used only by x86 and m68k
> > thanks to commit 3ba9faedc180 ("char: nvram: disable on ARM").
> > 
> > The "generic" module cannot be used by x86 or m68k platforms because it
> > cannot co-exist with the "CMOS" module. One reason for that is the
> > CONFIG_GENERIC_NVRAM kludge in drivers/char/Makefile. Another reason is
> > that automatically loading the appropriate module would be impossible
> > because only one module can provide the char-major-10-144 alias.
> > 
> > A multi-platform kernel binary needs a single, generic module. With this
> > patch series, drivers/char/nvram.c becomes more generic and some of the
> > arch-specific code gets moved under arch/. The nvram module is then
> > usable by all m68k, powerpc and x86 platforms.
> > 
> > This allows for removal of drivers/char/generic_nvram.c as well as a
> > duplicate in arch/powerpc/kernel/nvram_64.c. By reducing the number of
> > /dev/nvram char misc device implementations, the number of bugs and
> > inconsistencies is also reduced.
> > 
> > This approach reduces inconsistencies between PPC32 and PPC64 and also
> > between PPC_PMAC and MAC. A uniform API has benefits for userspace.
> > 
> > For example, some error codes for some ioctl calls become consistent
> > across PowerPC platforms. The uniform API can potentially benefit any
> > bootloader that works across the various platforms having XPRAM
> > (e.g. Emile).
> > 
> > This patch series was tested on Atari, Mac, PowerMac (both 32-bit and
> > 64-bit) and ThinkPad hardware. AFAIK, it has not yet been tested on
> > pSeries or CHRP.
> > 
> > I think there are two possible merge strategies for this patch series.
> > The char misc maintainer could take the entire series. Alternatively,
> > the m68k maintainer could take patches 1 thru 16 (though some of these
> > have nothing to do with m68k) and after those patches reach mainline
> > the powerpc maintainer could take 17 thru 22.
> 
> I just took the whole series, thanks for doing this, looks good.
> 

Thanks, Greg.

I haven't seen any acks from powerpc maintainers yet...

-- 

> greg k-h
>