Re: [PATCH] Revert "ARM: Use armlinux_bootparams address for DTB"

[Maxime Ripard <maxime.ripard@free-electrons.com>]

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On Wed, Aug 07, 2013 at 04:06:24PM +0400, Alexander Shiyan wrote:
> > On Wed, Aug 07, 2013 at 01:55:42PM +0400, Alexander Shiyan wrote:
> > > > This patch placed the flattened devicetree to armlinux_bootparams.
> > > > armlinux_bootparams normally is at SDRAM_START + 0x100. The kernels
> > > > initial page tables are normally at SDRAM_START + 0x4000, so the
> > > > flattened devicetree gets overwritten once it exceeds 0x3f00 bytes
> > > > which is quite common.
> > > > 
> > > > Revert this patch for now once a better solution can be found
> > > 
> > > In such a case, tree may be placed immediately after the kernel?
> > > It can also serve as an automatic option "ARM_APPENDED_DTB".
> > 
> > That won't work either, since the DTB will be overwritten by the kernel
> > decompressor.
> 
> arch/arm/Kconfig:
> ...
> config ARM_APPENDED_DTB
> 	bool "Use appended device tree blob to zImage (EXPERIMENTAL)"
> 	depends on OF && !ZBOOT_ROM
> 	help
> 	  With this option, the boot code will look for a device tree binary
> 	  (DTB) appended to zImage
> 	  (e.g. cat zImage <filename>.dtb > zImage_w_dtb).
> ...
> 
> So, DTB is placed immediately after the kernel.

Yes, in the case where you have APPENDED_DTB, the decompressor relocates
the DTB before doing the decompression.

The trouble is when you don't have APPENDED_DTB enabled, when there is
no such relocation happening.

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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