EDAC: Add helper which returns the loaded platform driver

Only a single EDAC platform driver can be loaded. When ghes_edac is
enabled, an EDAC platform driver still attempts to register itself and
fails in edac_mc_add_mc().

Add edac_get_owner() so that EDAC platform drivers can check the owner
first.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Suggested-by: Borislav Petkov <bp@alien8.de>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/20170823225447.15608-5-toshi.kani@hpe.com
[ Massage commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/edac_mc.c

@@ -53,7 +53,7 @@ static LIST_HEAD(mc_devices);
  * Used to lock EDAC MC to just one module, avoiding two drivers e. g.
  *	apei/ghes and i7core_edac to be used at the same time.
  */
-static void const *edac_mc_owner;
+static const char *edac_mc_owner;
 
 static struct bus_type mc_bus[EDAC_MAX_MCS];
 
@@ -701,6 +701,11 @@ struct mem_ctl_info *edac_mc_find(int idx)
 }
 EXPORT_SYMBOL(edac_mc_find);
 
+const char *edac_get_owner(void)
+{
+	return edac_mc_owner;
+}
+EXPORT_SYMBOL_GPL(edac_get_owner);
 
 /* FIXME - should a warning be printed if no error detection? correction? */
 int edac_mc_add_mc_with_groups(struct mem_ctl_info *mci,

drivers/edac/edac_mc.h

@@ -128,6 +128,14 @@ struct mem_ctl_info *edac_mc_alloc(unsigned mc_num,
 				   unsigned sz_pvt);
 
 /**
+ * edac_get_owner - Return the owner's mod_name of EDAC MC
+ *
+ * Returns:
+ *	Pointer to mod_name string when EDAC MC is owned. NULL otherwise.
+ */
+extern const char *edac_get_owner(void);
+
+/*
  * edac_mc_add_mc_with_groups() - Insert the @mci structure into the mci
  *	global list and create sysfs entries associated with @mci structure.
  *