Re: RE: [PATCH v2 2/3] arm/dt: tegra: add dts file for paz00

[Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>]

On Sat, Oct 29, 2011 at 01:03:20PM +0200, Grant Likely wrote:
> On Sat, Oct 29, 2011 at 09:43:30AM +0100, Russell King - ARM Linux wrote:
> > On Fri, Oct 28, 2011 at 09:49:49AM -0700, Stephen Warren wrote:
> > > When boards boot from DT, there is no fixup function to override the
> > > bootloader's ATAGs. I also see a bunch of code to set up the memory
> > > information from DT e.g. setup_machine_fdt()'s call to:
> > > 
> > > 	of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> > > 
> > > ... but I assume that happens before the ATAGs are processed, and the
> > > buggy ATAGs end up overriding the information in the DT file.
> > 
> > As far as the uncompressed kernel is concerned, there is either ATAG
> > or DT information, never both.  If the boot loader provides ATAGs and
> > the zImage has a DT appended to it, the zImage decompressor merges the
> > ATAGs into the appended DT and passes the DT to the kernel.
> > 
> > So anyone who currently 'fixes' their broken boot loader via the fixup
> > function by directly manipulating the ATAGS is going to hit the DT
> > image instead.
> 
> Ugh.  Not pretty.  A platform could still have board specific fixup
> code that matches on the compatible string that deals with broken
> firmware ATAGs, but I don't think that is what we want to do.

No.  The point I was making is that by the time you get to the fixup
function with a DT or even into the uncompressed kernel, even if the
boot loader provided ATAGs, your ATAGs have long since been obliterated
and are no longer available.