Stefan Roese wrote:
Hi,
I am wondering how the device tree "chosen" node should be handled, if it already exists in the device tree blob given to U-Boot. When this node doesn't exist it gets created and everything is fine. But if it already exists, it doesn't get overwritten and the defaults from the device tree blob most of the time are not what I really want.
So I would like U-Boot to overwrite the existing chosen node. I discovered that the fdt_chosen() function already has this "force" parameter, but it is not set in the current U-Boot implementation. I would like to set it for my board ports and I am wondering how I should handle this. Should this be done via a compile switch (#define), or via an env variable, or...?
Any ideas/comments on this?
Thanks.
Best regards, Stefan
Hi Stefan,
Disclaimer: I am not a OF expert, I have not read the OF documentation cover to cover and do not understand many implications of what I've read, much less what I have _not_ read.
1) I believe the /chosen node should be auto-created.
2) As you point out, if the /chosen node already exists the current code bails out and doesn't change anything. This was done as a very badly misguided attempt to make libfdt things work like bd_t things. The granularity should be on the individual properties, not on /chosen. I consider this a bug and have it on my "todo" list to fix (actually, I had created a patch, but I need to rebase and publish it).
http://www.denx.de/wiki/view/UBoot/UBootFdtInfo#Outstanding_Patches
"Unpublished patch of JerryVanBaren, implementing a suggestion by Scott Wood to make the /chosen handling finer grained: if the /chosen node exists, currently u-boot-fdt bails out. A better methodology is to not overwrite pre-existing properties on a per-property basis, so if /chosen exists but a necessary /chosen/property doesn't, it gets created. Good idea, but not published and poorly tested at the moment."
Best regards, gvb