On Thu, 22 May 2014 10:50:48 +0100
Ian Campbell <[email protected]> wrote:

> On Wed, 2014-05-21 at 14:39 +0300, Riku Voipio wrote:
> > 
> > Hi,
> > 
> > I've collected a list of where people install their dtb files these
> > days;
> > 
> > https://wiki.linaro.org/Platform/DeviceTreeConsolidation
> > 
> > 
> > Every distribution has a slightly different variation of install
> > location, which is not good - we can't tell end users that "this is
> > the place you can expect to find your device tree files regardless
> > of what distribution you choose".  Some questions I have here
> > before we proceed discussing what would be the standardized
> > location:
> > 
> > 
> > 1) Anything missing of the pros and cons of different locations?
> 
> FWIW Debian will now arrange for the correct DTB for the platform to
> be installed as /boot/dtb-$(uname -r) as well as the /usr/lib
> location.
> 
> WRT the use of `uname -r` and DTB as stable ABI, might it be sensible
> to declare a search path type arrangement? i.e.
> try /path/with-uname-r/dtb then /path/dtb ? For example people might
> consider packaging
> https://git.kernel.org/cgit/linux/kernel/git/devicetree/devicetree-rebasing.git
> which doesn't have a uname in it.
> 
> > 2) Are you interested in moving to a standardized location if
> > cross-distro list proposes one?
> 
> Installing the dtb for the current platform into some known location
> easily accessed from bootloaders seems reasonable enough.
> 
> I'm more or less ambivalent about installing all of the possible DTB
> files in a similar location though. I'm not sure what the use case for
> that is. Wouldn't you also need to standardise on the dtb filename for
> each platform and effectively make that ABI?

u-boot 2014.04 added an option to the syslinux config support for a
fdtdir entry which is a directory where u-boot can find the dtbs it
relies on the platforms u-boot having a variable fdtfile to know which
file to load for the platform

the syslinux config file is looked for in /boot/extlinux/extlinux.conf
and /extlinux/extlinux.conf 

contents is

timeout 20
totaltimeout 9000


default=Fedora (3.15.0-0.rc5.git2.9.fc21.armv7hl) 21 (Rawhide)
label Fedora (3.15.0-0.rc5.git3.1.fc21.armv7hl) 21 (Rawhide)
        kernel /vmlinuz-3.15.0-0.rc5.git3.1.fc21.armv7hl
        fdtdir /dtb-3.15.0-0.rc5.git3.1.fc21.armv7hl/
        append console=ttymxc0,115200 
root=UUID=7ee85ed8-de4a-4779-8658-2daed0d35e97 ro rhgb quiet LANG=en_US.UTF-8
        initrd /initramfs-3.15.0-0.rc5.git3.1.fc21.armv7hl.img

label Fedora (3.15.0-0.rc5.git2.9.fc21.armv7hl) 21 (Rawhide)
        kernel /vmlinuz-3.15.0-0.rc5.git2.9.fc21.armv7hl
        fdtdir /dtb-3.15.0-0.rc5.git2.9.fc21.armv7hl/
        append console=ttymxc0,115200 
root=UUID=7ee85ed8-de4a-4779-8658-2daed0d35e97 ro rhgb quiet LANG=en_US.UTF-8
        initrd /initramfs-3.15.0-0.rc5.git2.9.fc21.armv7hl.img


So in theory you can pull a sdcard or hdd from one machine and boot it
in another, in practice as so many vendors do not ship u-boot on some
kind of local storage you need to put the right u-boot into the disk
first.


Dennis

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