linux-kernel - Re: [PATCH 2/3] Kbuild: Implement CONFIG_UIMAGE_KERNEL

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Message-ID: <4F57C4C6.2070602@wwwdotorg.org>
Date:	Wed, 07 Mar 2012 13:27:50 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
CC:	Michal Marek <mmarek@...e.cz>, linux-arch@...r.kernel.org,
	Michal Simek <monstr@...str.eu>,
	Guan Xuetao <gxt@...c.pku.edu.cn>,
	Mike Frysinger <vapier@...too.org>, nico@...xnic.net,
	linux-sh@...r.kernel.org, microblaze-uclinux@...e.uq.edu.au,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Paul Mundt <lethal@...ux-sh.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	sparclinux@...r.kernel.org, Russell King <linux@....linux.org.uk>,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>
Subject: Re: [PATCH 2/3] Kbuild: Implement CONFIG_UIMAGE_KERNEL_NOLOAD

On 03/07/2012 11:36 AM, Jean-Christophe PLAGNIOL-VILLARD wrote:
> On 11:40 Wed 07 Mar     , Stephen Warren wrote:
>> On 03/07/2012 11:08 AM, Jean-Christophe PLAGNIOL-VILLARD wrote:
>>> On 17:30 Tue 06 Mar     , Stephen Warren wrote:
>>>> This allows the user to use U-Boot's mkimage's -T kernel_noload option
>>>> if their arch Kconfig allows it, and they desire.
>>>>
>>>> Signed-off-by: Stephen Warren <swarren@...dotorg.org>
>>>> ---
>>>> The next patch enables this new CONFIG_ALLOW_ option for ARM. I assume
>>>> that some other architectures will also be able to enable it, but I'm
>>>> not familiar enough with any to know which.
>>> I'm going to repeat. I don't think any impromevent here.
>>>
>>> with no specific kernel load address the uImage for is useless/
>>
>> No, the whole point of this type of kernel image is that it doesn't need
>> a specific load address; the kernel zImage can run from anywhere in RAM
>> (provided AUTO_ZRELADDR is enabled, subject to some slight
>> restrictions), and hence the uImage doesn't need to be loaded to or
>> moved to any particular location.
>>
>> The scripts that U-Boot runs determine where the image gets loaded into
>> memory.
>
> so instead of spending time on the uImage add simply the support the zImage to
> U-Boot as this AUTO_ZRELADDR have 0 advantage compare to the zImage

Thinking more about this, I guess the reliance on AUTO_ZRELADDR is wrong
here; Russell, Nico, is the ARM decompressor fully position-independent
irrespective of the AUTO_ZRELADDR setting. That setting just determines
where the decompressor writes its output, not what address the
decompressor can run at, right? So, this KERNEL_NOLOAD feature could be
enabled in all cases on ARM, not only when AUTO_ZRELADDR is enabled.

As such to address Jean-Christophe's most recent comment above, this
patch isn't about adding support for AUTO_ZRELADDR, but for U-Boot's
kernel_noload feature, so comparisons should be drawn between
kernel_noload uImages and zImage, not between AUTO_ZRELADDR and zImage.

In other words:

We already have and need ZRELADDR no matter what, for reasons unrelated
to U-Boot/uImage.

Patch 1 in this series is just consolidating duplicate definitions, and
doesn't introduce any new features, so I think hope you think it's a
good thing no matter what anyone thinks about U-Boot/uImage.

I assume you're only arguing about patches 2 and 3?
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