Re: Booting Linux Kernel without bootloader

On Aug 3, 2006, at 9:34 AM, Grant Likely wrote:

On 8/3/06, Milton Miller [off-list ref] wrote:

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On Tue Aug  1 2006 11:17:41 PM CDT,  Grant Likely  wrote:

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On 7/25/06, Clint Thomas [off-list ref] wrote:

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Basically, the system I want linux running on does not require the
initialization of hardware that U-boot provides, or at least it 

does not

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need it to boot the linux kernel. I want to load an uncompressed 

linux

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kernel into memory and start the execution of the kernel, without 

using any

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kind of bootloader. Is this possible? Or does linux need some 

kind of

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firmware or other software to tell it to start executing? Thanks 

for any

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info you might have.

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You could use the bootwrapper that is in the kernel source tree
(zImage).  If a zImage's entry point is at the execution entry 

point,

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then it will start the Linux kernel correctly.  However, it is 

still a

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compressed image.

The boot wrapper is a reference implementation, not a required piece 
of the
boot sequence.

...

I agree.  However, the original post sounded to me like he was looking
for a canned solution.  I know zImage isn't exactly what he asked for
because it is a compressed image, but it does achieve the *effect* he
asked for.

Actually the existing zImage will not do that, it requires a client
interface to allocate memory, etc.  There are alternates available
but they are not yet merged.

I am curious as to the source of his requirements.  ie. what is
loading the kernel into ram?  Where is it coming from?

That would be useful to help suggest alternatives.

I've got a similar situation on my Virtex-4 platform.  The FPGA takes
care of all device initialization.  However, the kernel is loaded of a
CF card via a *slow* JTAG interface.  Loading an uncompressed image is
more time consuming than loading a compressed image and uncompressing
it in software.

This is often the case.  However, if its loaded via some kind of DMA 
access
from a higher powered cpu then loading the uncompressed kernel could be
the fastest way.  Since we don't know we can only mention things to
consider as we state what can be done.

milton