Re: Early kernel hang with big DTB appended

[Tomasz Figa <t.figa@samsung.com>]

Hi Bryan,

Thanks for your reply.

On Thursday 03 of January 2013 13:40:43 Bryan Evenson wrote:
> > -----Original Message-----
> > From: linux-arm-kernel-bounces@lists.infradead.org [mailto:linux-arm-
> > kernel-bounces@lists.infradead.org] On Behalf Of Tomasz Figa
> > Sent: Thursday, January 03, 2013 10:55 AM
> > To: devicetree-discuss@lists.ozlabs.org
> > Cc: linux-samsung-soc@vger.kernel.org; linux@arm.linux.org.uk;
> > nico@linaro.org; kgene.kim@samsung.com; thomas.abraham@linaro.org;
> > bones@secretlab.ca; linux-arm-kernel@lists.infradead.org
> > Subject: Early kernel hang with big DTB appended
> > 
> > Hi,
> > 
> > I'm observing strange behavior when booting 3.8-rc1 and -rc2 with
> > appended DTB. The kernel hangs very early when the DTB is bigger than
> > some threshold somewhere around 24 KiB. With fullest possible low
> > level
> > UART debugging (and printk patched to use printascii) I'm receiving
> > following
> > output:
> > 
> > Uncompressing Linux... done, booting the kernel.
> > Booting Linux on physical CPU 0xa00
> > Linux version 3.8.0-rc1-00073-gdf6efca-dirty (t.figa@amdc1227) (gcc
> > version 4.5.2 (Gentoo 4.5.2 p1.2, pie-0.4.5) ) #2 SMP PREEMPT Thu Jan
> > 3
> > 15:37:35 CET 2013
> > CPU: ARMv7 Processor [413fc090] revision 0 (ARMv7), cr=10c53c7d
> > CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction
> > cache
> > 
> > I tested on two Exynos-based boards (exynos4210-trats and one internal
> > exynos4412-based board) and same happens on both.
> > 
> > Do you have any ideas?
> 
> Tomasz,
> 
> Sounds to me like the DTB is not being fully written to memory or that
> it isn't being fully read from memory.  I've had similar problems when
> I placed the DTB too close to the end of flash and not all of the DTB
> was written to flash.

I'm using CONFIG_ARM_APPENDED_DTB, as it eases testing a bit, because DTB 
is built into the resulting uImage for u-boot (appended after zImage) and 
it does not require OF-aware versions of u-boot.

Also the uImage is stored on an ext4 partition as a regular file, so I 
would exclude any storage issues.

> 
> If you load a debug build of U-Boot, I believe there are a number of
> debug messages related to loading the device tree that U-Boot prints. 
> Then you can at least verify that U-Boot is loading the entire device
> tree.

The u-boot I have is not OF-aware, so it just prints the standard messages 
about loading the uImage.

P.S. With Nicolas' hint about image load address I managed to work around 
the issue and limit the scope of code where the bug might exist. Please 
see my reply to Nicolas' post.

Best regards,
-- 
Tomasz Figa
Samsung Poland R&D Center
SW Solution Development, Linux Platform