csky: MMU and page table management

This patch adds files related to memory management and here is our
memory-layout:

   Fixmap       : 0xffc02000 – 0xfffff000       (4 MB - 12KB)
   Pkmap        : 0xff800000 – 0xffc00000       (4 MB)
   Vmalloc      : 0xf0200000 – 0xff000000       (238 MB)
   Lowmem       : 0x80000000 – 0xc0000000       (1GB)

abiv1 CPU (CK610) is VIPT cache and it doesn't support highmem.
abiv2 CPUs are all PIPT cache and they could support highmem.

Lowmem is directly mapped by msa0 & msa1 reg, and we needn't setup
memory page table for it.

Link:https://lore.kernel.org/lkml/20180518215548.GH17671@n2100.armlinux.org.uk/
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>

arch/csky/mm/init.c

@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/bug.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/signal.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/pagemap.h>
+#include <linux/ptrace.h>
+#include <linux/mman.h>
+#include <linux/mm.h>
+#include <linux/bootmem.h>
+#include <linux/highmem.h>
+#include <linux/memblock.h>
+#include <linux/swap.h>
+#include <linux/proc_fs.h>
+#include <linux/pfn.h>
+
+#include <asm/setup.h>
+#include <asm/cachectl.h>
+#include <asm/dma.h>
+#include <asm/pgtable.h>
+#include <asm/pgalloc.h>
+#include <asm/mmu_context.h>
+#include <asm/sections.h>
+#include <asm/tlb.h>
+
+pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
+pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned_bss;
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
+						__page_aligned_bss;
+EXPORT_SYMBOL(empty_zero_page);
+
+void __init mem_init(void)
+{
+#ifdef CONFIG_HIGHMEM
+	unsigned long tmp;
+
+	max_mapnr = highend_pfn;
+#else
+	max_mapnr = max_low_pfn;
+#endif
+	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
+
+	free_all_bootmem();
+
+#ifdef CONFIG_HIGHMEM
+	for (tmp = highstart_pfn; tmp < highend_pfn; tmp++) {
+		struct page *page = pfn_to_page(tmp);
+
+		/* FIXME not sure about */
+		if (!memblock_is_reserved(tmp << PAGE_SHIFT))
+			free_highmem_page(page);
+	}
+#endif
+	mem_init_print_info(NULL);
+}
+
+#ifdef CONFIG_BLK_DEV_INITRD
+void free_initrd_mem(unsigned long start, unsigned long end)
+{
+	if (start < end)
+		pr_info("Freeing initrd memory: %ldk freed\n",
+			(end - start) >> 10);
+
+	for (; start < end; start += PAGE_SIZE) {
+		ClearPageReserved(virt_to_page(start));
+		init_page_count(virt_to_page(start));
+		free_page(start);
+		totalram_pages++;
+	}
+}
+#endif
+
+extern char __init_begin[], __init_end[];
+
+void free_initmem(void)
+{
+	unsigned long addr;
+
+	addr = (unsigned long) &__init_begin;
+
+	while (addr < (unsigned long) &__init_end) {
+		ClearPageReserved(virt_to_page(addr));
+		init_page_count(virt_to_page(addr));
+		free_page(addr);
+		totalram_pages++;
+		addr += PAGE_SIZE;
+	}
+
+	pr_info("Freeing unused kernel memory: %dk freed\n",
+	((unsigned int)&__init_end - (unsigned int)&__init_begin) >> 10);
+}
+
+void pgd_init(unsigned long *p)
+{
+	int i;
+
+	for (i = 0; i < PTRS_PER_PGD; i++)
+		p[i] = __pa(invalid_pte_table);
+}
+
+void __init pre_mmu_init(void)
+{
+	/*
+	 * Setup page-table and enable TLB-hardrefill
+	 */
+	flush_tlb_all();
+	pgd_init((unsigned long *)swapper_pg_dir);
+	TLBMISS_HANDLER_SETUP_PGD(swapper_pg_dir);
+	TLBMISS_HANDLER_SETUP_PGD_KERNEL(swapper_pg_dir);
+
+	asid_cache(smp_processor_id()) = ASID_FIRST_VERSION;
+
+	/* Setup page mask to 4k */
+	write_mmu_pagemask(0);
+}