x86/amd_nb: Unexport amd_cache_northbridges()

amd_cache_northbridges() is exported by amd_nb.c and is called by
amd64-agp.c and amd64_edac.c modules at module_init() time so that NB
descriptors are properly cached before those drivers can use them.

However, the init_amd_nbs() initcall already does call
amd_cache_northbridges() unconditionally and thus makes sure the NB
descriptors are enumerated.

That initcall is a fs_initcall type which is on the 5th group (starting
from 0) of initcalls that gets run in increasing numerical order by the
init code.

The module_init() call is turned into an __initcall() in the MODULE=n
case and those are device-level initcalls, i.e., group 6.

Therefore, the northbridges caching is already finished by the time
module initialization starts and thus the correct initialization order
is retained.

Unexport amd_cache_northbridges(), update dependent modules to
call amd_nb_num() instead. While at it, simplify the checks in
amd_cache_northbridges().

  [ bp: Heavily massage and *actually* explain why the change is ok. ]

Signed-off-by: Muralidhara M K <muralimk@amd.com>
Signed-off-by: Naveen Krishna Chatradhi <nchatrad@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220324122729.221765-1-nchatrad@amd.com

arch/x86/include/asm/amd_nb.h

@@ -16,7 +16,6 @@ extern const struct amd_nb_bus_dev_range amd_nb_bus_dev_ranges[];
 
 extern bool early_is_amd_nb(u32 value);
 extern struct resource *amd_get_mmconfig_range(struct resource *res);
-extern int amd_cache_northbridges(void);
 extern void amd_flush_garts(void);
 extern int amd_numa_init(void);
 extern int amd_get_subcaches(int);

arch/x86/kernel/amd_nb.c

@@ -188,7 +188,7 @@ int amd_smn_write(u16 node, u32 address, u32 value)
 EXPORT_SYMBOL_GPL(amd_smn_write);
 
 
-int amd_cache_northbridges(void)
+static int amd_cache_northbridges(void)
 {
 	const struct pci_device_id *misc_ids = amd_nb_misc_ids;
 	const struct pci_device_id *link_ids = amd_nb_link_ids;
@@ -210,14 +210,14 @@ int amd_cache_northbridges(void)
 	}
 
 	misc = NULL;
-	while ((misc = next_northbridge(misc, misc_ids)) != NULL)
+	while ((misc = next_northbridge(misc, misc_ids)))
 		misc_count++;
 
 	if (!misc_count)
 		return -ENODEV;
 
 	root = NULL;
-	while ((root = next_northbridge(root, root_ids)) != NULL)
+	while ((root = next_northbridge(root, root_ids)))
 		root_count++;
 
 	if (root_count) {
@@ -290,7 +290,6 @@ int amd_cache_northbridges(void)
 
 	return 0;
 }
-EXPORT_SYMBOL_GPL(amd_cache_northbridges);
 
 /*
  * Ignores subdevice/subvendor but as far as I can figure out

drivers/char/agp/amd64-agp.c

@@ -327,7 +327,7 @@ static int cache_nbs(struct pci_dev *pdev, u32 cap_ptr)
 {
 	int i;
 
-	if (amd_cache_northbridges() < 0)
+	if (!amd_nb_num())
 		return -ENODEV;
 
 	if (!amd_nb_has_feature(AMD_NB_GART))

drivers/edac/amd64_edac.c

@@ -4336,7 +4336,7 @@ static int __init amd64_edac_init(void)
 	if (!x86_match_cpu(amd64_cpuids))
 		return -ENODEV;
 
-	if (amd_cache_northbridges() < 0)
+	if (!amd_nb_num())
 		return -ENODEV;
 
 	opstate_init();