[PATCH] bootm: dont use internal oftree fallback by default

[Alexander Kurz]

On Mon, 5 Dec 2016, Uwe Kleine-König wrote:

> On Fri, Dec 02, 2016 at 10:46:38AM +0100, Lucas Stach wrote:
> > Am Donnerstag, den 01.12.2016, 19:55 +0100 schrieb Alexander Kurz:
> > > Booting via bootm offers several methods to load oftree data. When no
> > > dedicated oftree image is provided, barebox checks for the presence of
> > > its own internal oftree, assuming it as a good choice for boot.
> > > 
> > > This fallback method breaks the usecase when a modern OF-based barebox
> > > is used to boot a legacy ATAG dependent non OF based vendor provided kernel
> > > (e.g. ATAGs will be switched off).
> > > Unfortunately those kernels are being still actively shipped today.
> > > 
> > > Change barebox according to the principle of least surprise: when no
> > > oftree data is proactively configured, then perform a non-oftree boot.
> > > Make the fallback-use of the barebox internal oftree an opt-in feature.
> > > 
> > > Note: this will break boards where the boot process relied on this feature,
> > > e.g.: oftree based barebox plus oftree based kernel without an explicit
> > > given dts. For those boards global.bootm.internal_oftree_fallback=1 should
> > > be set.
> > > 
> > The least surprise on a modern oftree based kernel is that the firmware
> > (Barebox) provides the DT, if there isn't an explicit override.
> > 
> > So NACK on the patch in it's current form. If you have a board where you
> > know that the kernel doesn't play along, you may reverse this patch so
> > that you can set global.bootm.no_internal_oftree=1 in your board code.
> 
> Ack for the NAck. And AFAIK you can already today just do
> 
> 	oftree -f
> 
> before calling bootm to discard the internal dtb which should make
> barebox fall back to ATAG.
After flushing the DT, ATAGs get passed during boot,
this makes my patch obsolete now.

Thank you very much,
Alexander

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