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

Uwe Kleine-König u.kleine-koenig at pengutronix.de
Mon Dec 5 00:29:19 PST 2016

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.

Best regards

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

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