Subject: Re: [RFC] [PATCH] PowerPC: add more than 4MB kernel image size support to bootwarapper

From: Scott Wood <[email-masked]>
Date: Sun, 07 Oct 2007 20:31:46 -0500

Mark A. Greer wrote:
> Why?  Because its only safe to download a zImage to certain "safe" locations.
> Where those "safe" locations are vary by firmware, firmware version, and
> zImage size.  This is the issue we're discussing.

In theory, yes -- but in practice the odds of this particular heuristic 
choosing an unsuitable address seem slim.

> I've already explained _why_ the link address matters WRT where its downloaded.

Sorry, I was being a bit too pendantic with respect to the distinction 
between link and load address.

>>> Also, being able to control the link address (that is, the download
>>> address with some firmwares) is not a u-boot specific issue and we
>>> shouldn't make a u-boot specific solution.
>> How is this a u-boot specific solution?
> 
> Because the hoops being jumped through in the patch(es) are to make
> u-boot happy and no other firmware.

No, the "hoops" (which I don't think are sufficiently complicated to 
warrant such a name) are to address a generic issue with the bootwrapper 
-- it wants to put the kernel at zero.  It'd be really nice if, in the 
absense of a vmlinux_alloc method, the generic code would do an ordinary 
malloc() if there's not enough room at zero.

>> I'd much rather it be automatic than require the user to guess an
>> appropriate value (and be aware in the first place that it needs to be set).
> 
> Sure, automatic is nice; conjuring up the magic to make it work in all
> situations isn't.

I think this heuristic would work in most situations, so if we do add a 
manual override it should be an override, and not something that 
everybody has to put up with.

> Having the link address--and therefore the download address on some
> systems--mysteriously and uncontrollably jump around based on the zImage
> size is asking for trouble.

It's a source of potential issues, but I think "asking for trouble" is 
exaggerating somewhat.

-Scott