void mca_set_adapter_procfn (int slot, MCA_ProcFn procfn, void* proc_dev);
This sets up an information callback for /proc/mca/slot?. The function is called with the buffer, slot, and device pointer (or some equally informative context information, or nothing, if you prefer), and is expected to put useful information into the buffer. The adapter name, ID, and POS registers get printed before this is called though, so don't do it again.
This should be called with a NULL procfn when a module unregisters, thus preventing kernel crashes and other such nastiness.