[U-Boot] Booting non devicetree enabled kernels using u-boot build with CONFIG_OF_LIBFDT ?

[Hans de Goede]

Hi,

On 11/17/2014 03:52 PM, Tom Rini wrote:
> On Thu, Nov 13, 2014 at 07:38:50PM +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 11/13/2014 07:34 PM, Tom Rini wrote:
>>> On Thu, Nov 13, 2014 at 07:08:59PM +0100, Hans de Goede wrote:
>>>> Hi all,
>>>>
>>>> So as you know I've been working on getting mainline u-boot to boot the
>>>> older android derived linux-sunxi kernels, as some people need features
>>>> not yet in mainline, and I would like there to be only one u-boot for both.
>>>>
>>>> I had this working a while ago, but recently it broke, this is caused by
>>>> config_distro_defaults.h setting CONFIG_OF_LIBFDT, if I undef that
>>>> after including config_distro_defaults.h things work again.
>>>>
>>>> I do not know if CONFIG_OF_LIBFDT is a recent addition to config_distro_defaults.h,
>>>> or if something else broke things. But if I do not undef it, boot fails with:
>>>>
>>>> sun7i# bootm start 0x48000000
>>>> ## Booting kernel from Legacy Image at 48000000 ...
>>>>    Image Name:   Linux-3.4.75.sun7i+
>>>>    Image Type:   ARM Linux Kernel Image (uncompressed)
>>>>    Data Size:    3966672 Bytes = 3.8 MiB
>>>>    Load Address: 40008000
>>>>    Entry Point:  40008000
>>>>    Verifying Checksum ... OK
>>>> Could not find a valid device tree
>>>
>>> My hunch is that we've got more fall-out from Simon's re-org of the
>>> bootm code ages ago.  It should be valid to try and boot a kernel
>>> without a device tree and other parts of the code base (for example
>>> arch/arm/lib/bootm.c) still do a FDT-or-ATAGS dance for example.
>>
>> That is good news, because ideally upstream u-boot build with
>> OLD_SUNXI_KERNEL_COMPAT should be able to boot old disk images without
>> needing them to modify their boot.scr, which requiring bootm 0xfoo - -
>> would do.
>>
>> So maybe check if there is a third argument to bootm, and if there
>> is not still try the dance for finding one appended in various ways,
>> and if that fails continue normally (where as with the third
>> argument present this of course needs to stay an error) ?
> 
> So first, I have to take it back.  This isn't a behavior change
> introduced by Simon's re-org (Sorry Simon!).  This is a real long
> standing "feature".   I am agreeable to doing whatever the lowest impact
> change would be to allow a non-DT tree to boot with CONFIG_OF_LIBFDT
> set.   I'm thinking we turn the error into a warning (so that it's still
> clear to the user that they booted without a DT, for when they didn't
> mean to do that)

I was thinking along the same lines, except that when a third argument
is explicitly given to u-boot, and then we do not find a dt, that should
be treated as an error IMHO. I've put whipping up a patch for this on my
todo list.

> and instead of a hang we just don't do the follow-up
> steps. 

Actually not doing the follow-up steps (as in bootm execution steps) is what
we currently do. What we want to do is skip further dt processing / prepping,
but otherwise still continue with trying to boot the kernel.

> That should let all the existing scripts work, yes?

With the amendments done above, I think so, yes. But the proof is in the
pudding, iow I'll find out when I go work on that patch.

Regards,

Hans