make PHYS_OFFSET determined at run time (unfinished)

[Uwe Kleine-König]

On Wed, Jan 20, 2010 at 09:26:41AM +1300, Ryan Mallon wrote:
> Uwe Kleine-König wrote:
> > Hello,
> > 
> > I'm looking into making PHYS_OFFSET determined at run time.  I saw a
> > patch for it that already made it a few times on the list[1].
> > 
> > I'm not yet done, but first want to announce that I look into that to
> > prevent duplicate work---so if you intended to do the same let's look
> > together---and to post some clean up patches that are the result up to
> > now of my digging in the boot code.
> > 
> > I will send now three patches in reply to this mail, and later hopefully
> > more.
> > 
> > Best regards
> > Uwe
> > 
> > [1] e.g. http://thread.gmane.org/gmane.linux.ports.arm.kernel/53793/
> > 
> 
> One of the problems that got brought up previously was the 'make uImage'
> can end up generating unbootable images with runtime PHYS_OFFSET. The
> older format uImage's (pre 1.3.3) encode a load address (zrealaddr), so
> uImage's need to have a fixed load address encoded.
> 
> As I stated in the previous thread, this is _not_ a kernel issue,
> however it is no good having a kernel which contains support for two
> boards which boot from different address and then generating a uImage
> which can only boot on one of them without warning the user about this
> problem. Otherwise you are going to start getting "I did make uImage and
> my board won't boot" problems.
> 
> There are a few solutions to this problem:
> 1) Drop uImage make support and require users generate them manually.
> 2) Have a uImage offset config option to allow uImage users to specify
> what they want the load address to be. See:
> http://thread.gmane.org/gmane.linux.ports.arm.kernel/53151/focus=53230
> 3) Print an error if "make uImage" is run for a kernel which has more
> than one boot address (possible?)
> 4) Use FIT U-Boot images. This is supported from U-Boot 1.3.3 onwards,
> however a number of people are still using older U-Boots.
5) use a mkimage(gzip(Image))-Image instead of mkimage(zImage).
   ($(make uImage) creates the latter.)  See
   http://thread.gmane.org/gmane.linux.ports.arm.kernel/36547
   .  You need gzip support in U-Boot for that.
6) boot a zImage as pointed out by Ben.

My preference would be:

	- rename uImage to uzImage (probably with a deprecation window)
	- introduce uImagegz that creates a mkimage(gzip(Image))-Image
	- allow overriding the load address for uzImage
	- for uImagegz that don't have a fixed zreladdr require
	  specifing a loadaddr

Last time I suggested something like that Russell wasn't happy as no
boot loader different from U-Boot needs so much magic in the kernel
Makefile.  If it's only not wanting to hatch that part of the kernel,
I'd volunteer to do that.

Best regards
Uwe

-- 
Pengutronix e.K.                              | Uwe Kleine-König            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |