microblaze: Improve TLB calculation for small systems

Systems with small amount of memory need to be handled
differently. Linux can't allocate the whole 32MB with two TLBs
because then there is no MMU protection.

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/mm/init.c

@@ -398,10 +398,16 @@ asmlinkage void __init mmu_init(void)
 		machine_restart(NULL);
 	}
 
-	if ((u32) memblock.memory.regions[0].size < 0x1000000) {
-		printk(KERN_EMERG "Memory must be greater than 16MB\n");
+	if ((u32) memblock.memory.regions[0].size < 0x400000) {
+		printk(KERN_EMERG "Memory must be greater than 4MB\n");
 		machine_restart(NULL);
 	}
+
+	if ((u32) memblock.memory.regions[0].size < kernel_tlb) {
+		printk(KERN_EMERG "Kernel size is greater than memory node\n");
+		machine_restart(NULL);
+	}
+
 	/* Find main memory where the kernel is */
 	memory_start = (u32) memblock.memory.regions[0].base;
 	lowmem_size = memory_size = (u32) memblock.memory.regions[0].size;
@@ -462,11 +468,11 @@ void __init *early_get_page(void)
 		p = alloc_bootmem_pages(PAGE_SIZE);
 	} else {
 		/*
-		 * Mem start + 32MB -> here is limit
+		 * Mem start + kernel_tlb -> here is limit
 		 * because of mem mapping from head.S
 		 */
 		p = __va(memblock_alloc_base(PAGE_SIZE, PAGE_SIZE,
-					memory_start + 0x2000000));
+					memory_start + kernel_tlb));
 	}
 	return p;
 }