linux-kernel - Re: [PATCH V2 22/22] MIPS: Add multiplatform BMIPS target

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Date:	Mon, 17 Nov 2014 15:52:15 +0100
From:	Jonas Gorski <jogo@...nwrt.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Kevin Cernekee <cernekee@...il.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jon Fraser <jfraser@...adcom.com>, dtor@...omium.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 22/22] MIPS: Add multiplatform BMIPS target

On Mon, Nov 17, 2014 at 1:16 PM, Arnd Bergmann <arnd@...db.de> wrote:
> I still think this is different in the sense that ARM multiplatform
> support is about combining platforms from separate mach-* directories,
> while your approach was to rewrite multiple mach-* directories into
> a single new one that remains separate from the others. While this is
> a great improvement, it doesn't get you any closer to having a
> combined BMIPS+RALINK+JZ4740+ATH79 kernel for instance. I don't know
> if such a kernel is something that anybody wants, or if it's even
> technically possible.
>
> If you wanted to do that however, starting with BMIPS you'd have
> to make it possible to define a new platform without the
> arch/mips/include/asm/mach-bmips/ directory (this should be possible
> already, so the hardest part is done), replace all global function
> calls (arch_init_irq, prom_init, get_system_type,  ...) with generic
> platform-independent implementations or wrappers around per-platform
> callbacks, and move the Kconfig section for CONFIG_BMIPS_MULTIPLATFORM
> outside of the "System type" choice statement.
> Until you do that, your platform isn't "more multipliplatform" than
> the others really, it just abstracts the differences between some
> SoCs nicer than most.

I guess a big blocker for such a real mips multiplatform kernel is
that there is still no defined (standard) interface for passing a
device tree to the kernel from the bootlader on mips, unlike on arm
(at least I'm not aware of any). And unless there is one, having a
multiplatform kernel does not make much sense, as there is no sane way
to tell apart different platforms on boot. But maybe we should just
define a way, and require new platforms to use it ;-)


Jonas
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