arm64: Implement generic stage transitions for non-Tegra SoCs

The existing arm64 architecture code has been developed for the Tegra132
and Tegra210 SoCs, which only start their ARM64 cores in ramstage. It
interweaves the stage entry point with code that initializes a CPU (and
should not be run again if that CPU already ran a previous stage). It
also still contains some vestiges of SMP/secmon support (such as setting
up stacks in the BSS instead of using the stage-peristent one from
memlayout).

This patch splits those functions apart and makes the code layout
similar to how things work on ARM32. The default stage_entry() symbol is
a no-op wrapper that just calls main() for the current stage, for the
normal case where a stage ran on the same core as the last one. It can
be overridden by SoC code to support special cases like Tegra.

The CPU initialization code is split out into armv8/cpu.S (similar to
what arm_init_caches() does for ARM32) and called by the default
bootblock entry code. SoCs where a CPU starts up in a later stage can
call the same code from a stage_entry() override instead.

The Tegra132 and Tegra210 code is not touched by this patch to make it
easier to review and validate. A follow-up patch will bring those SoCs
in line with the model.

BRANCH=None
BUG=None
TEST=Booted Oak with a single mmu_init()/mmu_enable(). Built Ryu and
Smaug.

Change-Id: I28302a6ace47e8ab7a736e089f64922cef1a2f93
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: http://review.coreboot.org/12077
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/Kconfig

@@ -437,8 +437,8 @@ config HEAP_SIZE
 
 config STACK_SIZE
 	hex
-	default 0x0 if (ARCH_RAMSTAGE_ARM || ARCH_RAMSTAGE_MIPS || ARCH_RAMSTAGE_RISCV)
+	default 0x1000 if ARCH_X86
-	default 0x1000
+	default 0x0
 
 config MAX_CPUS
 	int

src/arch/arm64/Makefile.inc

@@ -33,16 +33,6 @@ ifeq ($(CONFIG_ARCH_ROMSTAGE_ARM64),y)
 CBFSTOOL_PRE1_OPTS = -m arm64 -s $(CONFIG_CBFS_SIZE)
 endif
 
-ifeq ($(CONFIG_ARCH_ARM64),y)
-stages_c = $(src)/arch/arm64/stages.c
-stages_o = $(obj)/arch/arm64/stages.o
-
-$(stages_o): $(stages_c) $(obj)/config.h
-	@printf "    CC         $(subst $(obj)/,,$(@))\n"
-	$(CC_arm) -I. $(CPPFLAGS_arm) -c -o $@ $< -marm
-
-endif
-
 ################################################################################
 # bootblock
 ################################################################################
@@ -55,9 +45,7 @@ $(obj)/arch/arm64/id.bootblock.o: $(obj)/build.h
 
 bootblock-y += boot.c
 bootblock-y += c_entry.c
-bootblock-y += stage_entry.S
 bootblock-y += cpu-stubs.c
-bootblock-y += stages.c
 bootblock-y += eabi_compat.c
 bootblock-y += transition.c transition_asm.S
 
@@ -89,7 +77,6 @@ verstage-y += eabi_compat.c
 verstage-y += ../../lib/memset.c
 verstage-y += ../../lib/memcpy.c
 verstage-y += ../../lib/memmove.c
-verstage-y += stages.c
 
 endif # CONFIG_ARCH_VERSTAGE_ARM64
 
@@ -101,9 +88,7 @@ ifeq ($(CONFIG_ARCH_ROMSTAGE_ARM64),y)
 
 romstage-y += boot.c
 romstage-y += c_entry.c
-romstage-y += stage_entry.S
 romstage-y += cpu-stubs.c
-romstage-y += stages.c
 romstage-y += div0.c
 romstage-y += eabi_compat.c
 romstage-y += memset.S
@@ -129,7 +114,6 @@ endif # CONFIG_ARCH_ROMSTAGE_ARM64
 ifeq ($(CONFIG_ARCH_RAMSTAGE_ARM64),y)
 
 ramstage-y += c_entry.c
-ramstage-y += stages.c
 ramstage-y += div0.c
 ramstage-y += eabi_compat.c
 ramstage-y += boot.c
@@ -137,11 +121,15 @@ ramstage-y += tables.c
 ramstage-y += memset.S
 ramstage-y += memcpy.S
 ramstage-y += memmove.S
-ramstage-y += stage_entry.S
 ramstage-y += cpu-stubs.c
 ramstage-$(CONFIG_ARM64_USE_ARM_TRUSTED_FIRMWARE) += arm_tf.c
 ramstage-y += transition.c transition_asm.S
 
+# TODO: Replace this with a simpler ramstage entry point in soc/nvidia/tegra*
+ifeq ($(CONFIG_SOC_NVIDIA_TEGRA132)$(CONFIG_SOC_NVIDIA_TEGRA210),y)
+ramstage-y += stage_entry.S
+endif
+
 rmodules_arm64-y += memset.S
 rmodules_arm64-y += memcpy.S
 rmodules_arm64-y += memmove.S

src/arch/arm64/armv8/Makefile.inc

@@ -26,6 +26,9 @@ armv8_asm_flags = $(armv8_flags)
 ################################################################################
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARMV8_64),y)
 
+ifneq ($(CONFIG_BOOTBLOCK_CUSTOM),y)
+bootblock-y += bootblock.S
+endif
 bootblock-y += cache.c
 bootblock-y += cache_helpers.S
 bootblock-y += cpu.S

src/arch/arm64/armv8/bootblock.S

@@ -1,7 +1,7 @@
 /*
  * Early initialization code for aarch64 (a.k.a. armv8)
  *
- * Copyright 2013  Google Inc.
+ * Copyright 2015 Google Inc.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -14,21 +14,23 @@
  * GNU General Public License for more details.
  */
 
-	.section ".id", "a", %progbits
+#include <arch/asm.h>
 
-	.globl __id_start
+ENTRY(_start)
-__id_start:
+	/* Initialize PSTATE, SCTLR and caches to clean state. */
-ver:
+	bl	arm64_init_cpu
-	.asciz COREBOOT_VERSION
-vendor:
-	.asciz CONFIG_MAINBOARD_VENDOR
-part:
-	.asciz CONFIG_MAINBOARD_PART_NUMBER
-.long __id_end - ver  /* Reverse offset to the vendor id */
-.long __id_end - vendor  /* Reverse offset to the vendor id */
-.long __id_end - part    /* Reverse offset to the part number */
-.long CONFIG_ROM_SIZE    /* Size of this romimage */
-	.globl __id_end
 
-__id_end:
+	/* Initialize stack with sentinel value to later check overflow. */
-.previous
+	ldr	x0, =_stack
+	ldr	x1, =_estack
+	ldr	x2, =0xdeadbeefdeadbeef
+stack_init_loop:
+	stp	x2, x2, [x0], #16
+	cmp	x0, x1
+	bne	stack_init_loop
+
+	/* Leave a line of beef dead for easier visibility in stack dumps. */
+	sub	sp, x0, #16
+
+	bl	main
+ENDPROC(_start)

src/arch/arm64/armv8/cpu.S

@@ -19,27 +19,40 @@
 
 /*
  * Bring an ARMv8 processor we just gained control of (e.g. from IROM) into a
- * known state regarding caches/SCTLR. Completely cleans and invalidates
+ * known state regarding caches/SCTLR/PSTATE. Completely cleans and invalidates
  * icache/dcache, disables MMU and dcache (if active), and enables unaligned
- * accesses, icache and branch prediction (if inactive). Clobbers x4 and x5.
+ * accesses, icache and branch prediction (if inactive). Clobbers R22 and R23.
  */
-ENTRY(arm_init_caches)
+ENTRY(arm64_init_cpu)
-	/* w4: SCTLR, return address: x8 (stay valid for the whole function) */
+	/* Initialize PSTATE (unmask all exceptions, select SP_EL0). */
-	mov	x8, x30
+	msr	SPSel, #0
-	/* XXX: Assume that we always start running at EL3 */
+	msr	DAIFClr, #0xf
-	mrs	x4, sctlr_el3
 
-	/* FIXME: How to enable branch prediction on ARMv8? */
+	/* TODO: This is where we'd put non-boot CPUs into WFI if needed. */
+
+	/* x22: SCTLR, return address: x23 (callee-saved by subroutine) */
+	mov	x23, x30
+	/* TODO: Assert that we always start running at EL3 */
+	mrs	x22, sctlr_el3
+
+	/* Activate ICache (12) already for speed during cache flush below. */
+	orr	x22, x22, #(1 << 12)
+	msr	sctlr_el3, x22
+	isb
 
 	/* Flush and invalidate dcache */
 	mov	x0, #DCCISW
 	bl	flush_dcache_all
 
 	/* Deactivate MMU (0), Alignment Check (1) and DCache (2) */
-	and	x4, x4, # ~(1 << 0) & ~(1 << 1) & ~(1 << 2)
+	and	x22, x22, # ~(1 << 0) & ~(1 << 1) & ~(1 << 2)
-	/* Activate ICache (12) already for speed */
+	/* Activate Stack Alignment (3) because why not */
-	orr	x4, x4, #(1 << 12)
+	orr	x22, x22, #(1 << 3)
-	msr	sctlr_el3, x4
+	/* Set to little-endian (25) */
+	and	x22, x22, # ~(1 << 25)
+	/* Deactivate write-xor-execute enforcement (19) */
+	and	x22, x22, # ~(1 << 19)
+	msr	sctlr_el3, x22
 
 	/* Invalidate icache and TLB for good measure */
 	ic	iallu
@@ -47,26 +60,5 @@ ENTRY(arm_init_caches)
 	dsb	sy
 	isb
 
-	ret	x8
+	ret	x23
-ENDPROC(arm_init_caches)
+ENDPROC(arm64_init_cpu)
-
-/* Based on u-boot transition.S */
-ENTRY(switch_el3_to_el2)
-	mov	x0, #0x5b1	/* Non-secure EL0/EL1 | HVC | 64bit EL2 */
-	msr	scr_el3, x0
-	msr	cptr_el3, xzr	/* Disable coprocessor traps to EL3 */
-	mov	x0, #0x33ff
-	msr	cptr_el2, x0	/* Disable coprocessor traps to EL2 */
-
-	/* Return to the EL2_SP2 mode from EL3 */
-	mov	x0, sp
-	msr	sp_el2, x0	/* Migrate SP */
-	mrs	x0, vbar_el3
-	msr	vbar_el2, x0	/* Migrate VBAR */
-	mrs	x0, sctlr_el3
-	msr	sctlr_el2, x0	/* Migrate SCTLR */
-	mov	x0, #0x3c9
-	msr	spsr_el3, x0	/* EL2_SP2 | D | A | I | F */
-	msr	elr_el3, x30
-	eret
-ENDPROC(switch_el3_to_el2)

src/arch/arm64/armv8/exception.c

@@ -36,6 +36,8 @@
 #include <console/console.h>
 #include <arch/lib_helpers.h>
 
+uint8_t exception_stack[0x200] __attribute__((aligned(16)));
+
 static const char *exception_names[NUM_EXC_VIDS] = {
 	[EXC_VID_CUR_SP_EL0_SYNC] = "_sync_sp_el0",
 	[EXC_VID_CUR_SP_EL0_IRQ] = "_irq_sp_el0",
@@ -193,19 +195,17 @@ static uint64_t test_exception(void)
 	return 0;
 }
 
-void exception_hwinit(void)
-{
-	exc_set_vbar();
-}
-
 void exception_init(void)
 {
-	/* Load the exception table. */
+	/* Load the exception table and initialize SP_EL3. */
-	exception_hwinit();
+	exception_init_asm(exception_stack + ARRAY_SIZE(exception_stack));
 
 	printk(BIOS_DEBUG, "ARM64: Exception handlers installed.\n");
 
+	/* Only spend time testing on debug builds that are trying to detect more errors. */
+	if (IS_ENABLED(CONFIG_FATAL_ASSERTS)) {
 		printk(BIOS_DEBUG, "ARM64: Testing exception\n");
 		test_exception();
 		printk(BIOS_DEBUG, "ARM64: Done test exception\n");
+	}
 }

src/arch/arm64/boot.c

@@ -71,3 +71,11 @@ void arch_prog_run(struct prog *prog)
 
 	doit(prog_entry_arg(prog));
 }
+
+#if !IS_ENABLED(CONFIG_SOC_NVIDIA_TEGRA132)
+/* Generic stage entry point. Can be overridden by board/SoC if needed. */
+__attribute__((weak)) void stage_entry(void)
+{
+	main();
+}
+#endif

src/arch/arm64/include/arch/header.ld

@@ -24,11 +24,7 @@ PHDRS
 	to_load PT_LOAD;
 }
 
-#if ENV_BOOTBLOCK
+#if ENV_BOOTBLOCK ||  ENV_RMODULE
-TARGET(binary)
-#endif
-
-#if ENV_RMODULE
 ENTRY(_start)
 #else
 ENTRY(stage_entry)

src/arch/arm64/include/arch/memlayout.h

@@ -22,13 +22,13 @@
 	REGION(ttb, addr, size, 4K) \
 	_ = ASSERT(size % 4K == 0, "TTB size must be divisible by 4K!");
 
-/* ARM64 stacks need 16-byte alignment. The ramstage will set up its own stacks
+/* ARM64 stacks need 16-byte alignment. */
- * in BSS, so this is only used for the SRAM stages. */
+#if !(IS_ENABLED(CONFIG_SOC_NVIDIA_TEGRA132) || \
-#ifdef __PRE_RAM__
+      IS_ENABLED(CONFIG_SOC_NVIDIA_TEGRA210))
 #define STACK(addr, size) \
 	REGION(stack, addr, size, 16) \
 	_ = ASSERT(size >= 2K, "stack should be >= 2K, see toolchain.inc");
-#else
+#else	/* Hack around old Tegra stage_entry.S implementation. TODO: remove */
 #define STACK(addr, size) REGION(preram_stack, addr, size, 16)
 #endif
 

src/arch/arm64/include/armv8/arch/exception.h

@@ -33,9 +33,11 @@
 #include <arch/transition.h>
 
 /* Initialize the exception handling on the current CPU. */
-void exception_hwinit(void);
 void exception_init(void);
 
+/* Initialize VBAR and SP_EL3. */
+void exception_init_asm(void *exception_stack_end);
+
 /*
  * Order matters for handling return values. The larger the value the higher
  * the precedence.

src/arch/arm64/stages.c

@@ -1,44 +0,0 @@
-/*
- * This file is part of the coreboot project.
- *
- * Copyright 2014 Google Inc.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; version 2 of the License.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- */
-
-/*
- * This file contains entry/exit functions for each stage during coreboot
- * execution (bootblock entry and ramstage exit will depend on external
- * loading).
- *
- * Entry points must be placed at the location the previous stage jumps
- * to (the lowest address in the stage image). This is done by giving
- * stage_entry() its own section in .text and placing it first in the
- * linker script.
- */
-
-#include <arch/stages.h>
-#include <arch/cache.h>
-
-/* we had marked 'doit' as 'noreturn'.
- * There is no apparent harm in leaving it as something we can return from, and in the one
- * case where we call a payload, the payload is allowed to return.
- * Hence, leave it as something we can return from.
- */
-void stage_exit(void *addr)
-{
-	void (*doit)(void) = addr;
-	/*
-	 * Most stages load code so we need to sync caches here. Should maybe
-	 * go into cbfs_load_stage() instead...
-	 */
-	cache_sync_instructions();
-	doit();
-}

src/arch/arm64/transition_asm.S

@@ -155,11 +155,18 @@ ENTRY(exc_exit)
 	eret
 ENDPROC(exc_exit)
 
-/* exc_set_vbar: Initialize the exception entry address in vbar */
+/*
-ENTRY(exc_set_vbar)
+ * exception_init_asm: Initialize VBAR and point SP_EL3 to exception stack.
+ * x0 = end of exception stack
+ */
+ENTRY(exception_init_asm)
+	msr	SPSel, #SPSR_USE_H
+	mov	sp, x0
+	msr	SPSel, #SPSR_USE_L
+
 	adr	x0, exc_vectors
 	write_current vbar, x0, x1
 	dsb	sy
 	isb
 	ret
-ENDPROC(exc_set_vbar)
+ENDPROC(exception_init_asm)

src/soc/nvidia/tegra132/Kconfig

@@ -17,6 +17,11 @@ config SOC_NVIDIA_TEGRA132
 
 if SOC_NVIDIA_TEGRA132
 
+# TODO: Remove after replacing arch/arm64/stage_entry.S
+config STACK_SIZE
+	hex
+	default 0x1000
+
 config MAINBOARD_DO_DSI_INIT
 	bool "Use dsi graphics interface"
 	depends on MAINBOARD_DO_NATIVE_VGA_INIT

src/soc/nvidia/tegra210/Kconfig

@@ -22,6 +22,11 @@ if SOC_NVIDIA_TEGRA210
 config CHROMEOS
 	select CHROMEOS_RAMOOPS_NON_ACPI
 
+# TODO: Remove after replacing arch/arm64/stage_entry.S
+config STACK_SIZE
+	hex
+	default 0x1000
+
 config MAINBOARD_DO_DSI_INIT
 	bool "Use dsi graphics interface"
 	depends on MAINBOARD_DO_NATIVE_VGA_INIT