linux-kernel - RE: [PATCH] arm/tegra: select AUTO

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Date:	Fri, 14 Oct 2011 14:01:51 -0700
From:	Stephen Warren <swarren@...dia.com>
To:	Nicolas Pitre <nico@...xnic.net>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"Colin Cross (ccross@...roid.com)" <ccross@...roid.com>,
	Erik Gilling <konkers@...roid.com>
Subject: RE: [PATCH] arm/tegra: select AUTO_ZRELADDR by default

Nicolas Pitre wrote at Friday, October 14, 2011 2:45 PM:
> On Fri, 14 Oct 2011, Stephen Warren wrote:
...
> > I did originally briefly look into getting U-Boot to boot a zImage, but
> > that looked like a far more invasive patch. There were rumours of some
> > chip's custom U-Boot already having such support, but I couldn't find
> > it, nor any evidence of such support in mainline U-Boot.
> 
> FRom my clone of the u-Boot repo:
> 
> $ git grep -l zImage
> README
> arch/sh/lib/zimageboot.c
> arch/x86/lib/zimage.c
> ...
> 
> Even the name of some of those files clearly hints zImage support.
> 
> In any case, loading zImage should be even simpler than loading uImage.
> It is the same as loading uImage except that you just have to skip the
> checking and relocating steps.

Just by way of background in case anyone is wondering why I wrote the
patch I did:

Those files both implement custom commands "zimageboot" and "zboot". I
was looking for integration with the existing "bootm" command.

The advantage of re-using "bootm" for this is that it already supports
all the stuff like setting up kernel command-lines, initrds, knowing how
to pass the FDT to the kernel, and whatever other OS-specific setup might
be required.

The disadvantage of adding zImage support to bootm is that I'd have to
teach a bunch of U-Boot image handling code about a new image format; it
already knows about "legacy uImage", "FIT" images, and I'd have to add a
third "zImage" format. Doing so would at least require adding a lot of
"case IMAGE_FORMAT_ZIMAGE" everywhere, but it'd probably be best to add
some kind of vtable for image formats to move all the image-format
knowledge into format-specific files, leaving the users of the images
with much smaller code.

I didn't feel like making such a large change. Hence, I chose to make a
small change to the existing uImage support.

Now admittedly I did say I didn't find any traces of zImage support, which
isn't what I'm saying here; I guess I forgot about the stuff I did find
soon after I chose the path of modifying the uImage formats.

-- 
nvpublic

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