Andres Salomon wrote:
On Wed, 11 Aug 2010 22:48:43 +0200 (CEST)
"Segher Boessenkool" <[email protected]> wrote:
I've run a comparison between OLPC's old OFW code (which mounts the
device-tree at /ofw, and makes use of the sparc code) versus the
code which I'm planning to send upstream (which mounts the
device-tree at /proc/device-tree, and makes use of PROC_DEVTREE).
The results are here:
[unit addresses are missing]
Any insight into the reasoning for this mangling?
It sounds to me like you're not putting the (textual representation
of the) unit address in the device_node->full_name field. How do
you fill that field?
Ah, that could very well be it. Note that the *old* OLPC code used the
'path_component_name' of device_node. The new code uses just 'name' in
pdt_build_full_name(), as path_component_name is #ifdef'd out
for !SPARC. I guess I'm not entirely sure why sparc used
path_component_name in the first place..
I think I understand the situation. The guess that I articulated on IRC
is essentially correct. The (human-readable) text representation of the
unit address - i.e. the stuff after "@" - is parent-bus-specific. The
numerical representation of a unit address is easily determined - it is
the first "#address-cells" cells of the "reg" property. But the
rendering of that into ASCII is not as obvious.
A live OF environment gets the text representation by calling the parent
bus's "decode-unit" method with the numerical representation as an
argument. (In the other direction, the "encode-unit" method goes from
text to numerical.) There's an easy way to get that effect via the
client interface - just call "package-to-path" on the phandle, and OF
will return the full pathname in canonical form.
If you look in arch/sparc/kernel/prom.c:sparc32_path_component() you'll
see what is going on. That routine derives a "n...@address" string
using a heuristic described in this comment:
/* The following routines deal with the black magic of fully naming a
* node.
*
* Certain well known named nodes are just the simple name string.
*
* Actual devices have an address specifier appended to the base name
* string, like this "f...@addr". The "addr" can be in any number of
* formats, and the platform plus the type of the node determine the
* format and how it is constructed.
*
* For children of the ROOT node, the naming convention is fixed and
* determined by whether this is a sun4u or sun4v system.
*
* For children of other nodes, it is bus type specific. So
* we walk up the tree until we discover a "device_type" property
* we recognize and we go from there.
*/
As I described above, it's not really black magic; extract the numerical
form of the unit address and pass it to the parent's encode-unit method
. Either someone didn't know about that, or perhaps they had some
reason for not using it. It's certainly do-able during the phase while
OF is still alive.
In the non-SPARC case, I think the code was dealing with a flattened
device tree, where the node name had already been pre-digested to
include the @addr suffix. In that case, decoding the unit address into
the text representation was somebody else's problem, so there was no
(non-SPARC) Linux code to handle it.
The "proc_of.c" code that I wrote in Dec 2006 uses the package-to-path
method mentioned above, getting the "n...@addr" representation
(package-to-path returns the full path, but you can easily extract just
the tail component with strrchr(path, '/'))
The code that fills in full_name:
dp->full_name = pdt_build_full_name(dp);
static char * __init pdt_build_full_name(struct device_node *dp)
{
int len, ourlen, plen;
char *n;
plen = strlen(dp->parent->full_name);
ourlen = strlen(fetch_node_name(dp));
len = ourlen + plen + 2;
n = prom_early_alloc(len);
strcpy(n, dp->parent->full_name);
if (!of_is_root_node(dp->parent)) {
strcpy(n + plen, "/");
plen++;
}
strcpy(n + plen, fetch_node_name(dp));
return n;
}
#if defined(CONFIG_SPARC)
static inline const char *fetch_node_name(struct device_node *dp)
{
return dp->path_component_name;
}
#else
static inline const char *fetch_node_name(struct device_node *dp)
{
return dp->name;
}
#endif
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