xtensa: initialize MMU before jumping to reset vector

When reset is simulated MMU need to be brought into its initial state,
because that's what bootloaders/OS kernels assume. This is especially
important for MMUv3 because TLB state when the kernel is running is
significatly different from its reset state.

With this change it is possible to boot linux and get back to U-Boot
repeatedly.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/setup.c

@@ -551,6 +551,114 @@ subsys_initcall(topology_init);
 
 void cpu_reset(void)
 {
+#if XCHAL_HAVE_PTP_MMU
+	local_irq_disable();
+	/*
+	 * We have full MMU: all autoload ways, ways 7, 8 and 9 of DTLB must
+	 * be flushed.
+	 * Way 4 is not currently used by linux.
+	 * Ways 5 and 6 shall not be touched on MMUv2 as they are hardwired.
+	 * Way 5 shall be flushed and way 6 shall be set to identity mapping
+	 * on MMUv3.
+	 */
+	local_flush_tlb_all();
+	invalidate_page_directory();
+#if XCHAL_HAVE_SPANNING_WAY
+	/* MMU v3 */
+	{
+		unsigned long vaddr = (unsigned long)cpu_reset;
+		unsigned long paddr = __pa(vaddr);
+		unsigned long tmpaddr = vaddr + SZ_512M;
+		unsigned long tmp0, tmp1, tmp2, tmp3;
+
+		/*
+		 * Find a place for the temporary mapping. It must not be
+		 * in the same 512MB region with vaddr or paddr, otherwise
+		 * there may be multihit exception either on entry to the
+		 * temporary mapping, or on entry to the identity mapping.
+		 * (512MB is the biggest page size supported by TLB.)
+		 */
+		while (((tmpaddr ^ paddr) & -SZ_512M) == 0)
+			tmpaddr += SZ_512M;
+
+		/* Invalidate mapping in the selected temporary area */
+		if (itlb_probe(tmpaddr) & 0x8)
+			invalidate_itlb_entry(itlb_probe(tmpaddr));
+		if (itlb_probe(tmpaddr + PAGE_SIZE) & 0x8)
+			invalidate_itlb_entry(itlb_probe(tmpaddr + PAGE_SIZE));
+
+		/*
+		 * Map two consecutive pages starting at the physical address
+		 * of this function to the temporary mapping area.
+		 */
+		write_itlb_entry(__pte((paddr & PAGE_MASK) |
+				       _PAGE_HW_VALID |
+				       _PAGE_HW_EXEC |
+				       _PAGE_CA_BYPASS),
+				 tmpaddr & PAGE_MASK);
+		write_itlb_entry(__pte(((paddr & PAGE_MASK) + PAGE_SIZE) |
+				       _PAGE_HW_VALID |
+				       _PAGE_HW_EXEC |
+				       _PAGE_CA_BYPASS),
+				 (tmpaddr & PAGE_MASK) + PAGE_SIZE);
+
+		/* Reinitialize TLB */
+		__asm__ __volatile__ ("movi	%0, 1f\n\t"
+				      "movi	%3, 2f\n\t"
+				      "add	%0, %0, %4\n\t"
+				      "add	%3, %3, %5\n\t"
+				      "jx	%0\n"
+				      /*
+				       * No literal, data or stack access
+				       * below this point
+				       */
+				      "1:\n\t"
+				      /* Initialize *tlbcfg */
+				      "movi	%0, 0\n\t"
+				      "wsr	%0, itlbcfg\n\t"
+				      "wsr	%0, dtlbcfg\n\t"
+				      /* Invalidate TLB way 5 */
+				      "movi	%0, 4\n\t"
+				      "movi	%1, 5\n"
+				      "1:\n\t"
+				      "iitlb	%1\n\t"
+				      "idtlb	%1\n\t"
+				      "add	%1, %1, %6\n\t"
+				      "addi	%0, %0, -1\n\t"
+				      "bnez	%0, 1b\n\t"
+				      /* Initialize TLB way 6 */
+				      "movi	%0, 7\n\t"
+				      "addi	%1, %9, 3\n\t"
+				      "addi	%2, %9, 6\n"
+				      "1:\n\t"
+				      "witlb	%1, %2\n\t"
+				      "wdtlb	%1, %2\n\t"
+				      "add	%1, %1, %7\n\t"
+				      "add	%2, %2, %7\n\t"
+				      "addi	%0, %0, -1\n\t"
+				      "bnez	%0, 1b\n\t"
+				      /* Jump to identity mapping */
+				      "jx	%3\n"
+				      "2:\n\t"
+				      /* Complete way 6 initialization */
+				      "witlb	%1, %2\n\t"
+				      "wdtlb	%1, %2\n\t"
+				      /* Invalidate temporary mapping */
+				      "sub	%0, %9, %7\n\t"
+				      "iitlb	%0\n\t"
+				      "add	%0, %0, %8\n\t"
+				      "iitlb	%0"
+				      : "=&a"(tmp0), "=&a"(tmp1), "=&a"(tmp2),
+					"=&a"(tmp3)
+				      : "a"(tmpaddr - vaddr),
+					"a"(paddr - vaddr),
+					"a"(SZ_128M), "a"(SZ_512M),
+					"a"(PAGE_SIZE),
+					"a"((tmpaddr + SZ_512M) & PAGE_MASK)
+				      : "memory");
+	}
+#endif
+#endif
 	__asm__ __volatile__ ("movi	a2, 0\n\t"
 			      "wsr	a2, icountlevel\n\t"
 			      "movi	a2, 0\n\t"