amd64_edac: Fix single-channel setups

It can happen that configurations are running in a single-channel mode
even with a dual-channel memory controller, by, say, putting the DIMMs
only on the one channel and leaving the other empty. This causes a
problem in init_csrows which implicitly assumes that when the second
channel is enabled, i.e. channel 1, the struct dimm hierarchy will be
present. Which is not.

So always allocate two channels unconditionally.

This provides for the nice side effect that the data structures are
initialized so some day, when memory hotplug is supported, it should
just work out of the box when all of a sudden a second channel appears.

Reported-and-tested-by: Roger Leigh <rleigh@debian.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/amd64_edac.c

@@ -2470,8 +2470,15 @@ static int amd64_init_one_instance(struct pci_dev *F2)
 	layers[0].size = pvt->csels[0].b_cnt;
 	layers[0].is_virt_csrow = true;
 	layers[1].type = EDAC_MC_LAYER_CHANNEL;
-	layers[1].size = pvt->channel_count;
+
+	/*
+	 * Always allocate two channels since we can have setups with DIMMs on
+	 * only one channel. Also, this simplifies handling later for the price
+	 * of a couple of KBs tops.
+	 */
+	layers[1].size = 2;
 	layers[1].is_virt_csrow = false;
+
 	mci = edac_mc_alloc(nid, ARRAY_SIZE(layers), layers, 0);
 	if (!mci)
 		goto err_siblings;