Using CONFIG_PHYSICAL_START

Using CONFIG_PHYSICAL_START

[Meador Inge]

Hi Kumar,

Quick question about the support for booting at a non-zero base address 
(as committed here: 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=37dd2badcfcec35f5e21a0926968d77a404f03c3). 
  Is booting from a non-zero address as simple as changing 
"CONFIG_PHYSICAL_START" (assuming it meets the alignment constraints, of 
course)?

For example, I want to boot from a non-zero address on the P1022DS.  I 
should just be able to change "CONFIG_PHYSICAL_START" to, say, 
0x08000000, and it should work, right?  Any other bits that need to be 
done (i.e. U-Boot or device tree magic)?

-- 
Meador Inge     | meador_inge AT mentor.com
Mentor Embedded | http://www.mentor.com/embedded-software

Re: Using CONFIG_PHYSICAL_START

[Scott Wood]

On Wed, 16 Feb 2011 12:00:25 -0600
Meador Inge <meador_inge@mentor.com> wrote:

> Hi Kumar,
> 
> Quick question about the support for booting at a non-zero base address 
> (as committed here: 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=37dd2badcfcec35f5e21a0926968d77a404f03c3). 
>   Is booting from a non-zero address as simple as changing 
> "CONFIG_PHYSICAL_START" (assuming it meets the alignment constraints, of 
> course)?

Another option is to turn on CONFIG_RELOCATABLE.  Note that you'll still
have the same alignment constraints; it doesn't generate a truly relocatable
binary (the effective addresses are fixed).  But you don't have to specify
the physical address at compile-time.  This allows you to use the same
kernel image for multiple AMP partitions.

> For example, I want to boot from a non-zero address on the P1022DS.  I 
> should just be able to change "CONFIG_PHYSICAL_START" to, say, 
> 0x08000000, and it should work, right?  Any other bits that need to be 
> done (i.e. U-Boot or device tree magic)?

You'll want the memory node adjusted for your restricted address range
(I'm assuming that this is why you want to start at non-zero, and that
you're not trying to have the kernel be located in the middle of its
partition).

There are some special u-boot variables (bootm_low/bootm_size) that govern
placement of the kernel, fdt, etc.

-Scott

Re: Using CONFIG_PHYSICAL_START

[Meador Inge]

On 02/16/2011 01:24 PM, Scott Wood wrote:
> On Wed, 16 Feb 2011 12:00:25 -0600
> Meador Inge<meador_inge@mentor.com>  wrote:
>
>> Hi Kumar,
>>
>> Quick question about the support for booting at a non-zero base address
>> (as committed here:
>> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=37dd2badcfcec35f5e21a0926968d77a404f03c3).
>>    Is booting from a non-zero address as simple as changing
>> "CONFIG_PHYSICAL_START" (assuming it meets the alignment constraints, of
>> course)?
>
> Another option is to turn on CONFIG_RELOCATABLE.  Note that you'll still
> have the same alignment constraints; it doesn't generate a truly relocatable
> binary (the effective addresses are fixed).  But you don't have to specify
> the physical address at compile-time.  This allows you to use the same
> kernel image for multiple AMP partitions.
>
>> For example, I want to boot from a non-zero address on the P1022DS.  I
>> should just be able to change "CONFIG_PHYSICAL_START" to, say,
>> 0x08000000, and it should work, right?  Any other bits that need to be
>> done (i.e. U-Boot or device tree magic)?
>
> You'll want the memory node adjusted for your restricted address range
> (I'm assuming that this is why you want to start at non-zero, and that
> you're not trying to have the kernel be located in the middle of its
> partition).
>
> There are some special u-boot variables (bootm_low/bootm_size) that govern
> placement of the kernel, fdt, etc.


Thanks Scott.  I should have looked in the u-boot docs.  There are very 
clear instructions on how to setup an AMP environment in 
'.../doc/README.mpc8572ds' 
(http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=doc/README.mpc8572ds;h=06dab596bea52ab8d8c2ba89d86f793cc4881ccb;hb=HEAD).


> -Scott
>
>


-- 
Meador Inge     | meador_inge AT mentor.com
Mentor Embedded | http://www.mentor.com/embedded-software