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On Tue, 06 Aug 2013 07:53:14 -0500
Rob Herring <[email protected]> wrote:

> On 08/05/2013 10:53 PM, Andy Green wrote:
> > On 6 August 2013 11:05, Rob Herring <[email protected]> wrote:
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> >> On 08/05/2013 04:41 PM, Dennis Gilmore wrote:
> >>> Hi all,
> >>>
> >>> As part of the unified features in u-boot thread I said that I
> >>> would work to get distros to agree to a common location that
> >>> u-boot will be able to assume exists for it to transparently load
> >>> dtbs from for us.
> >>>
> >>> I would like to propose /boot/dtb/
> >>>
> >>> I think it needs to be in /boot/ to allow for booting from systems
> >>> with / and /boot on separate partitions. I believe Ubuntu and
> >>> hence Debian put them in /lib somewhere today.  Fedora puts them
> >>> in /boot/dtb-<kernel version>. im not sure where the other distros
> >>> put them.
> >>
> >> A DTB should not be tied to a kernel version. I realize that is a
> >> reality for some boards, but lets not encourage that. There are
> >> also plans to remove dts files from the kernel.
> >>
> >>>
> >>> I think that until they are decoupled from the kernel Fedora would
> >>> have /boot/dtb be a symlink to the latest installed kernel. once
> >>> its decoupled it would be the location where the dtbs are
> >>> installed.
> >>
> >> If /boot/dtb is THE dtb to use, does more than that need to be
> >> specified (at least from a bootloader perspective).
> > 
> > If I understood you correctly, that'd be needlessly limiting one
> > image to one board.
> > 
> > Consider an SD Card + CONFIG_ARCH_MULTIPLATFORM kernel you can pull
> > out and plug in to use on a variety of different boards, the
> > bootloader would need to identify the correct dtb and pass it to the
> > kernel.
> 
> Ah, right. I misread this.
> 
> So do we assume the dtb file names are known by the bootloader for a
> board or standardized in some way?

Yes, u-boot today on omap had a find_fdt function that provides the
name for the expected dtb for the board that its running on. as part of
the unified u-boot platform ive proposed, u-boot would transparently
load the dtb for us and pass it to the kernel. just like highbank does
today.

Dennis
> Rob
> 
> > U-Boot is bound up with compile-time decisions about targeting a
> > single board at the moment, but if we're talking about long term
> > decisions like /boot/dtb/ just like ARM isn't the only consideration
> > U-Boot is not the only bootloader.
> > 
> > Once kernels capable of running a single binary on many platforms
> > are common (they're already workable) pressure for the bootloader
> > to do likewise will increase.  So it'd be a shame to block that by
> > choosing a dtb convention that assumes there's only one on the
> > image.
> > 
> > -Andy
> > 
> 
> 
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