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

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Date:	Mon, 17 Nov 2014 21:40:50 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Kevin Cernekee <cernekee@...il.com>
Cc:	Ralf Baechle <ralf@...ux-mips.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jon Fraser <jfraser@...adcom.com>,
	Dmitry Torokhov <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>,
	Jonas Gorski <jonas.gorski@...il.com>
Subject: Re: [PATCH V2 22/22] MIPS: Add multiplatform BMIPS target

On Monday 17 November 2014 11:39:02 Kevin Cernekee wrote:
> On Mon, Nov 17, 2014 at 10:46 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Monday 17 November 2014 09:01:02 Kevin Cernekee wrote:
> >> > 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.
> >>
> >> Right.  The other question is how much support for legacy non-DT
> >> bootloaders really belongs in a true multiplatform kernel, as this
> >> stuff gets hairy fast.
> >
> > Yes, that's why I suggested following PowerPC rather than ARM in this
> > regard.  If you move the boot loader abstraction into the decompressor
> > instead of the platform code, you can avoid a lot of the problems.
> 
> One possible complication: for BCM63xx/BCM7xxx (MIPS) there is no
> decompressor in the kernel.  The firmware loads an ELF image into
> memory and jumps directly to kernel_entry.
> 

Right, that complicates it a bit, but is there a reason why a decompressor
would be hard to do, or would be considered a bad thing?
There is already generic decompressor code in arch/mips/boot/compressed/
that I would assume you could use without firmware changes. Are you
worried about boot time overhead?

	Arnd
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