On 01/12/2012 12:00 PM, Simon Glass wrote:
Some devices can deal with multiple compatible properties. The devices need to know which nodes to bind to which features. For example an I2C driver which supports two different controller types will want to know which type it is dealing with in each case.
The new fdtdec_add_aliases_for_id() function deals with this by allowing the driver to search for additional compatible nodes for a different ID. It can then detect the new ones and perform appropriate processing.
Another option considered was to return a tuple (node offset, compat id) and have the function be passed a list of compatible IDs. This is more overhead for the common case though. We may add such a function later if more drivers in U-Boot require it.
+int fdtdec_add_aliases_for_id(const void *blob, const char *name,
enum fdt_compat_id id, int *node_list, int maxcount)
...
@@ -232,11 +238,13 @@ int fdtdec_find_aliases_for_id(const void *blob, const char *name, * it as done. */ if (fdtdec_get_is_enabled(blob, node)) {
if (node_list[number])continue; node_list[number] = node; if (number >= num_found) num_found = number + 1;
nodes[j] = 0;
nodes[found] = 0;}
/* Add any nodes not mentioned by an alias */
Aren't those two changes really bug-fixes to the underlying patch rather than part of this enhancement?
I'm not convinced this patch is correct in all cases. It'll probably work fine for simply device-trees though. Consider the following case:
4 device nodes A: compat=i2c alias for usb0 B: compat=i2c no alias C: compat=i2c alias for usb2 D: compat=i2cx alias for usb1
First, we search for all compat=i2c, the list comes back:
0=A 1=B 2=C
Then we search for all compat=i2cx, the list comes back:
-1 -1 -1 D
So D's alias of 1 isn't honored even though if both IDs were searched for together, it would have been.
Also, what about the scenario where a driver searches for both nvidia,tegra20-i2c then later nvidia,tegra30-i2c, given that all the DT nodes are probably compatible with both?