powerpc/fadump: provide a helpful error message

fadump fails to register when there are holes in boot memory area.
Provide a helpful error message to the user in such case.
Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/fadump.c

@@ -130,6 +130,38 @@ int is_fadump_active(void)
 	return fw_dump.dump_active;
 }
 
+/*
+ * Returns 1, if there are no holes in boot memory area,
+ * 0 otherwise.
+ */
+static int is_boot_memory_area_contiguous(void)
+{
+	struct memblock_region *reg;
+	unsigned long tstart, tend;
+	unsigned long start_pfn = PHYS_PFN(RMA_START);
+	unsigned long end_pfn = PHYS_PFN(RMA_START + fw_dump.boot_memory_size);
+	unsigned int ret = 0;
+
+	for_each_memblock(memory, reg) {
+		tstart = max(start_pfn, memblock_region_memory_base_pfn(reg));
+		tend = min(end_pfn, memblock_region_memory_end_pfn(reg));
+		if (tstart < tend) {
+			/* Memory hole from start_pfn to tstart */
+			if (tstart > start_pfn)
+				break;
+
+			if (tend == end_pfn) {
+				ret = 1;
+				break;
+			}
+
+			start_pfn = tend + 1;
+		}
+	}
+
+	return ret;
+}
+
 /* Print firmware assisted dump configurations for debugging purpose. */
 static void fadump_show_config(void)
 {
@@ -457,6 +489,10 @@ static int register_fw_dump(struct fadump_mem_struct *fdm)
 			" dump. Hardware Error(%d).\n", rc);
 		break;
 	case -3:
+		if (!is_boot_memory_area_contiguous())
+			pr_err("Can't have holes in boot memory area while "
+			       "registering fadump\n");
+
 		printk(KERN_ERR "Failed to register firmware-assisted kernel"
 			" dump. Parameter Error(%d).\n", rc);
 		err = -EINVAL;