Hi David,
David Gibson wrote:
On Thu, Mar 01, 2007 at 09:01:24AM -0500, Jerry Van Baren wrote:
Hi all,
This is a Request for Advice.
First off, for those on both the u-boot and linuxppc-dev lists, sorry for cross posting. :-)
Git repo pointers... libfdt hacks: http://www.cideas.us/cgi-bin/gitweb.cgi?p=linux/libfdt.git;a=summary u-boot hacks: http://www.cideas.us/cgi-bin/gitweb.cgi?p=u-boot/u-boot-mpc83xx;a=summary
[snip]
- Not capturing libfdt in the u-boot repo makes it more difficult for
integrating it with and maintaining it in u-boot, I'm not sure how to actually do it in a useful/usable manner.
I think ultimately, you'll have to pull libfdt into the u-boot sources. libfdt is supposed to run in many possible environments, and there's no realistic way it can be compiled independently of thost environments.
That said, any changes to the guts of libfdt that you need should go upstream (in the end; right now, there are bureaucratic problems with that, more below). That should reduce things to a one way pull, with some trivial tweaks to integrate with the u-boot environment.
OK, I figured as much, but was hoping for a miracle.
There are three problem areas with libfdt:
- The official Makefile is stand-alone which doesn't work well with
u-boot. I took the expedient route for the PoC of simply replacing it with a u-boot style Makefile from a different lib* subdirectory. There should be a better way.
I think it might well be necessary to replace the Makefile for building libfdt into other packages. It would be nice to avoid that if possible, but a sensible method is not obvious to me.
OK, no surprise.
- The official libfdt uses two header files that are not in u-boot. I
"fixed" this by substituting u-boot headers with equivalent functionality.
- I need to address this and see what the best compromise for header
files is... a) If the u-boot headers are acceptable for the stand-alone version of libfdt, that would be the simplest. b) It may be more effective to add the necessary linux headers to u-boot. c) We could use #ifdefs to conditionally include the right files. (but does u-boot have a distinctive configuration def? Probably...)
Ok, the way this is supposed to work is that the environment into which you're building should provide a replacement version of libfdt_env.h. The supplied version of libfdt_env.h is just for userland builds. u-boot's version will obviously use u-boot headers instead of standard library headers.
I should provide a comprehensive list of what libfdt_env.h needs to provide, but I haven't gotten around to it. From memory it's basically just the fixed-with integer types, a smallish subset of the str*() and mem*() functions, and the endian conversion functions.
I've really tried to keep libfdt's environment dependencies down, so I suggest you just start with an empty libfdt_env.h and add stuff based on the error messages until the compiler stops whinging about undefined things. It shouldn't take long.
Yes, all the functionality is in both linux headers and u-boot headers that it stole^Winherited from linux. The problem is, the set is disjoint. If libfdt is willing to change its headers to use linux/types.h, asm/byteorder.h, and linux/string.h, the problem would go away:
fdt.h: -#include <stdint.h> +#include <linux/types.h>
libfdt_env.h: -#include <stdint.h> -#include <string.h> -#include <endian.h> -#include <byteswap.h> +#include <linux/types.h> +#include <asm/byteorder.h> +#include <linux/string.h>
Note that asm/byteorder.h provides __be32_to_cpu(x) and friends, which can be used directly rather than having to synthesize swap/noswap (i.e. bswap_32(x)) based on #if __BYTE_ORDER == __BIG_ENDIAN. They can be used directly, or fdt32_to_cpu and friends can be defined in terms of__be32_to_cpu(x) and friends: +#define fdt32_to_cpu(x) __be32_to_cpu(x) +#define cpu_to_fdt32(x) __cpu_to_be32(x) +#define fdt64_to_cpu(x) __be64_to_cpu(x) +#define cpu_to_fdt64(x) __cpu_to_be64(x)
When I did the above change and tried to compile it natively under linux, there were problems with unresolved types. I did not pursue the resolution of the problem since I am currently concentrating on u-boot usage.
- I added a "fdt_next_tag()" function to fdt_ro.c to allow me to step
through the blob's tags: uint32_t fdt_next_tag(const void *fdt, int offset, int *nextoffset, char **namep);
This is similar to "_fdt_next_tag()" (a "private" function, note the leading underscore) in fdt.c, but with a related but different purpose - the "_fdt_next_tag()" steps through _node_ tags (skipping property tags) where I need to step through all tags sequentially.
Um... no. _fdt_next_tag() steps through all tags (how else could it be used internally to find properties...?). If you really need this, we can change the function to be exported, which I've considered before. However, what are you using this function for? I had some node and property traversal functions on the drawing board.
Yes, I copied and augmented _fdt_next_tag():
uint32_t fdt_next_tag(const void *fdt, int offset, int *nextoffset, char **namep)
to give me a pointer to the node name for node tags and property name for property tags. Now that I have it working, it would be trivial to change the calls to _fdt_next_tag() to instead call fdt_next_tag() passing NULL for the new fourth parameter **namep. ;-)
The reason I need it, I'm printing an unknown tree by stepping through the tree discovering the node and property names. I need to have fdt_next_tag() return the *name* of the node/property as well as the tag so that I can print and indent for nodes or look up the property value and print the name=value combination.
Usability trivia for David: libfdt distinguishes between nodes and properties, which makes sense since that is how the fdt is structured. From a usability standpoint, however, it is annoying to have to separate the property name from the node, find the node, then find the property. I will probably create Yet Another Function: int fdt_split(char *path, char **property); Call it with a path string and the function will separate it into the node portion and the property name. If the path is invalid, it will return an error. If the path is a node, it will set **property to NULL and return the node's offset. If the path is a property, it will return the owning node's offset and set the **property pointer to point to the start of the property portion of the path (i.e. the next character after the last '/').
I don't like combining property and node name into a single path, because technically the property names occupy a different namespace from subnode names. Insane though it is, there exist some Apple device trees where a node has both a property and a subnode of the same name.
Oh gaak! What I hear you saying... if you have node a with subnode b and property b, subnode b has a property c: /a => node /a/b => node /a/b => property (inside node a) /a/b/c => property (inside node b)
Where I am right now is I created a new function fdt_fullpath_offset:
int fdt_fullpath_offset(const void *fdt, const char *path, char **prop);
which will return the _node_ /a/b in the gaak illustration above. It looks up nodes until it either runs out of path to look up or there is an error. On a lookup error, it tries again with the last part of the path used as a property name. As a result, if you pass in /a it will return the node "a", if you pass in /a/b it will return the _node_ "b". This is unchanged behavior compared to fdt_path_offset(). (Getting property "b" is unchanged: you would have to look up node /a with either fdt_fullpath_offset(... "/a" ...) or fdt_path_offset(... "/a" ...) and then use that offset with fdt_property() to get the property "b".)
I've changed the original fdt_path_offset() to simply call fdt_fullpath_offset() passing in NULL for **prop and everything (should) work the same as before ("should" because I haven't debugged it yet).
For my u-boot commands, I have "fdt get <prop>" and "fdt print <node>" and was going to consolidate them into one, but the gaak illustration says I should _not_ consolidate them. (Trivia: my "fdt print" of "/" and "/a" will (should anyway ;-) print the gaak tree properly.)
What are the odds that someone will pull an Apple on hardware supported by u-boot? Hmmm... extra code to handle stupidity.
Best regards, gvb