powerpc/32s: automatically allocate BAT in setbat()

If no BAT is given to setbat(), select an available BAT.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a212bd36fbd6179e0929b6c727febc35132ac25c.1568665466.git.christophe.leroy@c-s.fr

arch/powerpc/mm/book3s32/mmu.c

@@ -251,9 +251,18 @@ void __init setbat(int index, unsigned long virt, phys_addr_t phys,
 {
 	unsigned int bl;
 	int wimgxpp;
-	struct ppc_bat *bat = BATS[index];
+	struct ppc_bat *bat;
 	unsigned long flags = pgprot_val(prot);
 
+	if (index == -1)
+		index = find_free_bat();
+	if (index == -1) {
+		pr_err("%s: no BAT available for mapping 0x%llx\n", __func__,
+		       (unsigned long long)phys);
+		return;
+	}
+	bat = BATS[index];
+
 	if ((flags & _PAGE_NO_CACHE) ||
 	    (cpu_has_feature(CPU_FTR_NEED_COHERENT) == 0))
 		flags &= ~_PAGE_COHERENT;