[U-Boot-Users] Warning for mpc8360emds users: fdt-cmd from u-boot-fdt.git

Jerry Van Baren gvb.uboot at gmail.com
Thu Apr 5 13:00:15 CEST 2007

Wolfgang Denk wrote:
> In message <46146842.8060509 at gmail.com> you wrote:
>> If bootm edits/augments the FDT, the boot scripts/user has no chance to 
>> change the items it edits/augments (biggie: the chosen node), or even 
>> print it before linux is launched.  This defeats 90% of the purpose of 
>> the fdt command - allowing the user/script customize the blob before 
>> linux is launched.
> I agree that it should be *possible* to do this, if wanted.Similar
> like we can set up our own contents of thebootargs variable.
> On the other hand, bootm should do everything that is necessary to
> start a kernel without such interaction, if needed.
> Remember for example that bootm gets called automatically and without
> user interaction after download commands when "autostart" is  set  to
> "yes".
> Now assume we set "autostart" to "yes" nd  use  "dhcp"  to  load  and
> start a multifile image containing the FDT. This is required to work,
> to.
>> My reasoning is that you can string together (or script) the proper 
>> "fdt" commands to do what previously was done by "bootm" in one step, so 
>> we are losing a small bit of convenience and gaining a whole lot of 
>> flexibility.  As a for instance, currently/previously you had to 
> Agreed, but as an option, and without breaking compatibility of
> exiting methods.
>> Much, perhaps most, possibly even all of the current stuff that is 
>> wedged into bootm is or should be passed through the blob.
> I cannot parse this. Please explain what you have in mind.

Sorry, not my best example of English composition. :-/

What I was trying to say was that the linux bootargs (command line - in 
the chosen node), env variables (optional), and bd_t stuff (optional) is 
passed through the fdt blob now.  I was advocating that, by moving the 
creation of that stuff into the "fdt" command, we could simplify bootm. 
  Quite likely unrealistic, but it sounded good at the time.  Since then 
I got a solid 6 hrs sleep. ;-)

> Best regards,
> Wolfgang Denk

Andy Fleming sent a suggestion that is really growing on me:
> What if we made it so if there isn't a chosen node in the blob when
> bootm is called, it fills in a default one.  This prevents some odd
> failures, and allows people to continue using device trees in the
> current manner, while still enabling the extra flexibility. 

<foghorn> That boy, I say, that boy has a /point/. </foghorn>

This means that, if you use "fdt chosen" to create the chosen node, you 
will be able to look at it and edit it and bootm will do the Right 
Thing[tm].  If you don't bootm will still do the Right Thing[tm] and 
autogenerate the necessary nodes.


More information about the U-Boot mailing list