Messages in this thread | | | Date | Thu, 17 Oct 2013 17:44:07 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH] of/lib: Export fdt routines to modules |
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On 10/17/2013 04:51 PM, Michael Bohan wrote: > On Wed, Oct 16, 2013 at 09:54:27PM -0700, Guenter Roeck wrote: >> On 10/16/2013 05:27 PM, Michael Bohan wrote: >>> My motivation is actually to use the fdt format as a firmware. >>> I have a requirement to express driver metadata that's loadable >> >from the filesystem. This data is not reasonable to place in the >>> system Device Tree, since it's application specific and does not >>> actually describe hardware. The fact that the format chosen is >>> 'flattened device tree' is merely just a coincidence. >>> >> Still, what prevents you from unflattening it and just using the >> normal device tree functions as David suggested ? > > I'm assuming you're suggesting to use of_fdt_unflatten_tree()?
Yes, that was the idea.
> That's an interesting thought. I was planning to scan the fdt > only once and populate my own structures, but I suppose I could > use the of_* APIs equivalently. > > It seems there are some problems though. of_fdt_unflatten_tree() > does not return errors, and so for the purposes of my driver it > would not be sufficient to detect an invalid firmware image. > It does so, at least partially. If there is an error, it won't set the nodes pointer. Granted, that is not perfect, but it is at least a start. Ultimately, I considered it 'good enough' for my purpose (for devicetree overlays - see [1] below), as any missing mandatory properties or nodes are detected later when trying to actually read the properties. In my case, I also have a couple of validation properties to ensure that the overlay is acceptable (specifically I use 'compatible' and 'assembly-ids', but that is really a detail).
> Would people entertain changing this API > (and implicitly __unflatten_device_tree) to return errors? I'm > guessing the reason it's coded that way is because the normal > usecase is 'system boot', at which time errors aren't that > meaningful. > > Also, there's no way to free the memory that was allocated from > the unflatten process. May I add one? >
The patchset submitted by Pantelis Antoniou to add support for devicetree overlays adds this and other related functionality. See [1], specifically the patch titled "OF: Introduce utility helper functions". Not sure where that is going, though. It may need some cleanup to be accepted upstream. Copying Pantelis for comments.
I also updated the devicetree discussion list address to get comments from the experts.
Thanks, Guenter
[1] https://lkml.org/lkml/2013/1/4/276
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