nubus: Don't list slot resources by default

Some Nubus card ROMs contain many slot resources. A single Radius video
card produced well over a thousand entries under /proc/bus/nubus/.
Populating /proc/bus/nubus/ on a slow machine with several such cards
installed takes long enough that the user may think that the system is
wedged. All those procfs entries also consume significant RAM though
they are not normally needed (except by developers).
Omit these resources from /proc/bus/nubus/ by default and add a kernel
parameter to enable them when needed.
On the test machine, this saved 300 kB and 10 seconds.

Cc: Brad Boyer <[e-mail]>
Reviewed-by: Brad Boyer <[e-mail]>
Tested-by: Stan Johnson <[e-mail]>
Signed-off-by: Finn Thain <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Geert Uytterhoeven <[e-mail]>

drivers/nubus/nubus.c

···
 
 /* Globals */
 
+/* The "nubus.populate_procfs" parameter makes slot resources available in
+ * procfs. It's deprecated and disabled by default because procfs is no longer
+ * thought to be suitable for that and some board ROMs make it too expensive.
+ */
+bool nubus_populate_procfs;
+module_param_named(populate_procfs, nubus_populate_procfs, bool, 0);
+
 LIST_HEAD(nubus_func_rsrcs);
 
 /* Meaning of "bytelanes":
···
 			nubus_proc_add_rsrc(dir.procdir, &ent);
 			break;
 		default:
-			/* Local/Private resources have their own
-			   function */
-			nubus_get_private_resource(fres, dir.procdir, &ent);
+			if (nubus_populate_procfs)
+				nubus_get_private_resource(fres, dir.procdir,
+							   &ent);
 		}
 	}
 

drivers/nubus/proc.c

···
 {
 	char name[2];
 
-	if (!proc_bus_nubus_dir)
+	if (!proc_bus_nubus_dir || !nubus_populate_procfs)
 		return NULL;
 	snprintf(name, sizeof(name), "%x", board->slot);
 	return proc_mkdir(name, proc_bus_nubus_dir);
···
 	char name[9];
 	int lanes = board->lanes;
 
-	if (!procdir)
+	if (!procdir || !nubus_populate_procfs)
 		return NULL;
 	snprintf(name, sizeof(name), "%x", ent->type);
 	remove_proc_subtree(name, procdir);
···
 	char name[9];
 	struct nubus_proc_pde_data *pded;
 
-	if (!procdir)
+	if (!procdir || !nubus_populate_procfs)
 		return;
 
 	snprintf(name, sizeof(name), "%x", ent->type);
···
 	char name[9];
 	unsigned char *data = (unsigned char *)ent->data;
 
-	if (!procdir)
+	if (!procdir || !nubus_populate_procfs)
 		return;
 
 	snprintf(name, sizeof(name), "%x", ent->type);

include/linux/nubus.h

···
 
 /* Generic NuBus interface functions, modelled after the PCI interface */
 #ifdef CONFIG_PROC_FS
+extern bool nubus_populate_procfs;
 void nubus_proc_init(void);
 struct proc_dir_entry *nubus_proc_add_board(struct nubus_board *board);
 struct proc_dir_entry *nubus_proc_add_rsrc_dir(struct proc_dir_entry *procdir,