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

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Message-ID: <4E98B24A.2070408@gmail.com>
Date:	Fri, 14 Oct 2011 17:06:02 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Stephen Warren <swarren@...dia.com>
CC:	Nicolas Pitre <nico@...xnic.net>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Erik Gilling <konkers@...roid.com>,
	Arnd Bergmann <arnd@...db.de>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"Colin Cross (ccross@...roid.com)" <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm/tegra: select AUTO_ZRELADDR by default

On 10/14/2011 04:01 PM, Stephen Warren wrote:
> 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.
> 

FYI, this exact topic has been discussed on the Linaro weekly
boot-architecture call and list. The discussion has been more general in
terms of what can be done to make installing and updating kernels
easier/work for distros.

https://wiki.linaro.org/OfficeofCTO/BootArchitecture

Rob
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