[U-Boot] [RFC PATCH 2/3] ARM: mx6: ddr: add plugin-utils placeholder

[Eric Nelson <eric@nelint.com>]

Add entry points for saving the state of the machine at entry
from the Boot ROM and for restoring the state before a return.

Note that this needs some fixup before it's useful, so I'm
forwarding it as an RFC to solicit advice.

This placeholder is little more than a setjmp/longjmp that
saves the SP, LR and registers 0-9. Disassembling the ROM
for i.MX6DL and i.MX6SL shows that these are the only registers
used by the ROM on those SOCs.

Signed-off-by: Eric Nelson <eric@nelint.com>
---
 arch/arm/cpu/armv7/mx6/Makefile         |  2 +-
 arch/arm/cpu/armv7/mx6/ddr.c            |  4 ++++
 arch/arm/cpu/armv7/mx6/plugin-utils.S   | 24 ++++++++++++++++++++++++
 arch/arm/include/asm/arch-mx6/mx6-ddr.h | 19 +++++++++++++++++++
 4 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm/cpu/armv7/mx6/plugin-utils.S

diff --git a/arch/arm/cpu/armv7/mx6/Makefile b/arch/arm/cpu/armv7/mx6/Makefile
index 8af191d..d0d0103 100644
--- a/arch/arm/cpu/armv7/mx6/Makefile
+++ b/arch/arm/cpu/armv7/mx6/Makefile
@@ -8,5 +8,5 @@
 #
 
 obj-y	:= soc.o clock.o
-obj-$(CONFIG_SPL_BUILD)	     += ddr.o
+obj-$(CONFIG_SPL_BUILD)	     += ddr.o plugin-utils.o
 obj-$(CONFIG_MP)             += mp.o
diff --git a/arch/arm/cpu/armv7/mx6/ddr.c b/arch/arm/cpu/armv7/mx6/ddr.c
index 0cf391e..7f8e30d 100644
--- a/arch/arm/cpu/armv7/mx6/ddr.c
+++ b/arch/arm/cpu/armv7/mx6/ddr.c
@@ -1536,3 +1536,7 @@ void mx6_dram_cfg(const struct mx6_ddr_sysinfo *sysinfo,
 		hang();
 	}
 }
+
+#ifdef CONFIG_SPL_BUILD
+struct plugin_state plugin_state __attribute__((section(".data")));
+#endif
diff --git a/arch/arm/cpu/armv7/mx6/plugin-utils.S b/arch/arm/cpu/armv7/mx6/plugin-utils.S
new file mode 100644
index 0000000..c284a76
--- /dev/null
+++ b/arch/arm/cpu/armv7/mx6/plugin-utils.S
@@ -0,0 +1,24 @@
+/*
+ * Utility functions for executing as an i.MX plugin
+ *
+ * Copyright (c) 2016 Nelson Integration, LLC
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <asm-offsets.h>
+#include <config.h>
+#include <asm/system.h>
+#include <linux/linkage.h>
+
+ENTRY(save_boot_params)
+	ldr	r10, =plugin_state
+	stmia	r10, {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, fp, sp, lr}
+	b	save_boot_params_ret
+ENDPROC(save_boot_params)
+
+ENTRY(return_to_rom)
+	ldr	r10, =plugin_state
+	ldmia	r10, {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, fp, sp, lr}
+	bx	lr
+ENDPROC(return_to_rom)
diff --git a/arch/arm/include/asm/arch-mx6/mx6-ddr.h b/arch/arm/include/asm/arch-mx6/mx6-ddr.h
index 2a8d443..52420da 100644
--- a/arch/arm/include/asm/arch-mx6/mx6-ddr.h
+++ b/arch/arm/include/asm/arch-mx6/mx6-ddr.h
@@ -528,4 +528,23 @@ void mx6_dram_cfg(const struct mx6_ddr_sysinfo *,
 #define MX6_MMDC_P1_MPZQLP2CTL	0x021b485C
 #define MX6_MMDC_P1_MPMUR0	0x021b48b8
 
+#ifdef CONFIG_SPL_BUILD
+struct plugin_state {
+	uint32_t r0;
+	uint32_t r1;
+	uint32_t r2;
+	uint32_t r3;
+	uint32_t r4;
+	uint32_t r5;
+	uint32_t r6;
+	uint32_t r7;
+	uint32_t r8;
+	uint32_t r9;
+	uint32_t fp;
+	uint32_t sp;
+	uint32_t lr;
+};
+void return_to_rom(void);
+#endif
+
 #endif	/*__ASM_ARCH_MX6_DDR_H__ */
-- 
2.7.4