[U-Boot] [PATCH v4 25/26] sunxi: introduce RMR switch to enter payloads in 64-bit mode

[Andre Przywara]

The ARMv8 capable Allwinner A64 SoC comes out of reset in AArch32 mode.
To run AArch64 code, we have to trigger a warm reset via the RMR register,
which proceeds with code execution at the address stored in the RVBAR
register.
If the bootable payload in the FIT image is using a different
architecture than the SPL has been compiled for, enter it via this said
RMR switch mechanism, by writing the entry point address into the MMIO
mapped, writable version of the RVBAR register.
Then the warm reset is triggered via a system register write.
If the payload architecture is the same as the SPL, we use the normal
branch as usual.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
Acked-by: Maxime Ripard <maxime.ripard at free-electrons.com>
---
 arch/arm/mach-sunxi/Makefile     |  1 +
 arch/arm/mach-sunxi/spl_switch.c | 81 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 arch/arm/mach-sunxi/spl_switch.c

diff --git a/arch/arm/mach-sunxi/Makefile b/arch/arm/mach-sunxi/Makefile
index 7daba11..128091e 100644
--- a/arch/arm/mach-sunxi/Makefile
+++ b/arch/arm/mach-sunxi/Makefile
@@ -51,4 +51,5 @@ obj-$(CONFIG_MACH_SUN8I_A83T)	+= dram_sun8i_a83t.o
 obj-$(CONFIG_MACH_SUN8I_H3)	+= dram_sun8i_h3.o
 obj-$(CONFIG_MACH_SUN9I)	+= dram_sun9i.o
 obj-$(CONFIG_MACH_SUN50I)	+= dram_sun8i_h3.o
+obj-$(CONFIG_MACH_SUN50I)	+= spl_switch.o
 endif
diff --git a/arch/arm/mach-sunxi/spl_switch.c b/arch/arm/mach-sunxi/spl_switch.c
new file mode 100644
index 0000000..855379e
--- /dev/null
+++ b/arch/arm/mach-sunxi/spl_switch.c
@@ -0,0 +1,81 @@
+/*
+ * (C) Copyright 2016 ARM Ltd.
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include <common.h>
+#include <spl.h>
+
+#include <asm/io.h>
+#include <asm/barriers.h>
+
+static void __noreturn jump_to_image_native(struct spl_image_info *spl_image)
+{
+	typedef void __noreturn (*image_entry_noargs_t)(void);
+
+	image_entry_noargs_t image_entry =
+				(image_entry_noargs_t)spl_image->entry_point;
+
+	image_entry();
+}
+
+/*
+ * Do a warm-reset via the RMR register to enter the processor in a different
+ * execution mode. This allows to switch from AArch32 to AArch64 and vice
+ * versa. Execution starts at the address hold in the RVBAR register, which
+ * needs to be set before.
+ */
+static void __noreturn reset_rmr_switch(void)
+{
+#ifdef CONFIG_ARM64
+	__asm__ volatile ( "mrs	 x0, RMR_EL3\n\t"
+			   "bic  x0, x0, #1\n\t"   /* Clear enter-in-64 bit */
+			   "orr  x0, x0, #2\n\t"   /* set reset request bit */
+			   "msr  RMR_EL3, x0\n\t"
+			   "isb  sy\n\t"
+			   "nop\n\t"
+			   "wfi\n\t"
+			   "b    .\n"
+			   ::: "x0");
+#else
+	__asm__ volatile ( "mrc  15, 0, r0, cr12, cr0, 2\n\t"
+			   "orr  r0, r0, #3\n\t"   /* request reset in 64 bit */
+			   "mcr  15, 0, r0, cr12, cr0, 2\n\t"
+			   "isb\n\t"
+			   "nop\n\t"
+			   "wfi\n\t"
+			   "b    .\n"
+			   ::: "r0");
+#endif
+	while (1);	/* to avoid a compiler warning about __noreturn */
+}
+
+void __noreturn jump_to_image_no_args(struct spl_image_info *spl_image)
+{
+	if (spl_image->arch == IH_ARCH_DEFAULT) {
+		/*
+		 * If the image to be executed is using the same architecture
+		 * as we are currently running in, just branch to the target
+		 * address.
+		 */
+		debug("entering by branch\n");
+		jump_to_image_native(spl_image);
+	} else {
+		/*
+		 * If the target architecture and the current one differ, use
+		 * the RMR routine to change it.
+		 */
+		debug("entering by RMR switch\n");
+		/*
+		 * The start address at which execution continues after the
+		 * RMR switch is held in the RVBAR system register, which is
+		 * architecturally read-only.
+		 * Allwinner provides a writeable alias in MMIO space for it.
+		 */
+		writel(spl_image->entry_point, 0x17000a0);
+		DSB;
+		ISB;
+		reset_rmr_switch();
+	}
+}
-- 
2.8.2