rockchip: back-to-bootrom: replace assembly-implementation with C-code

The back-to-bootrom implementation for Rockchip has always relied on
the stack-pointer being valid on entry, so there was little reason to
have this as an assembly implementation.

This provides a new C-only implementation of save_boot_params and
back_to_bootrom (relying on setjmp/longjmp) and removes the older
assembly-only implementation.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Andy Yan <andy.yan@rock-chips.com>

arch/arm/include/asm/arch-rockchip/bootrom.h

@@ -1,5 +1,6 @@
 /*
  * (C) Copyright 2017 Heiko Stuebner <heiko@sntech.de>
+ * (C) Copyright 2017 Theobroma Systems Design und Consulting GmbH
  *
  * SPDX-License-Identifier:	GPL-2.0
  */
@@ -14,15 +15,27 @@
 extern u32 SAVE_SP_ADDR;
 
 /**
- * Hand control back to the bootrom to load another
- * boot stage.
+ * back_to_bootrom() - return to bootrom (for TPL/SPL), passing a
+ *                     result code
+ *
+ * Transfer control back to the Rockchip BROM, restoring necessary
+ * register context and passing a command/result code to the BROM
+ * to instruct its next actions (e.g. continue boot sequence, enter
+ * download mode, ...).
+ *
+ * This function does not return.
  */
-void back_to_bootrom(void);
+enum rockchip_bootrom_cmd {
+	/*
+	 * These can not start at 0, as 0 has a special meaning
+	 * for setjmp().
+	 */
 
-/**
- * Assembler component for the above (do not call this directly)
- */
-void _back_to_bootrom_s(void);
+	BROM_BOOT_NEXTSTAGE = 1,  /* continue boot-sequence */
+	BROM_BOOT_ENTER_DNL,      /* have BROM enter download-mode */
+};
+
+void back_to_bootrom(void);
 
 /**
  * Boot-device identifiers as used by the BROM

arch/arm/mach-rockchip/Makefile

@@ -8,8 +8,8 @@
 # this may have entered from ATF with the stack-pointer pointing to
 # inaccessible/protected memory (and the bootrom-helper assumes that
 # the stack-pointer is valid before switching to the U-Boot stack).
-obj-spl-$(CONFIG_ROCKCHIP_BROM_HELPER) += bootrom.o save_boot_param.o
-obj-tpl-$(CONFIG_ROCKCHIP_BROM_HELPER) += bootrom.o save_boot_param.o
+obj-spl-$(CONFIG_ROCKCHIP_BROM_HELPER) += bootrom.o
+obj-tpl-$(CONFIG_ROCKCHIP_BROM_HELPER) += bootrom.o
 
 obj-tpl-$(CONFIG_ROCKCHIP_RK3188) += rk3188-board-tpl.o
 obj-tpl-$(CONFIG_ROCKCHIP_RK3288) += rk3288-board-tpl.o

arch/arm/mach-rockchip/bootrom.c

@@ -6,11 +6,61 @@
 
 #include <common.h>
 #include <asm/arch/bootrom.h>
+#include <asm/setjmp.h>
+#include <asm/system.h>
+
+/*
+ * Force the jmp_buf to the data-section, as .bss will not be valid
+ * when save_boot_params is invoked.
+ */
+static jmp_buf brom_ctx __section(".data");
 
 void back_to_bootrom(void)
 {
 #if CONFIG_IS_ENABLED(LIBCOMMON_SUPPORT)
 	puts("Returning to boot ROM...\n");
 #endif
-	_back_to_bootrom_s();
+	longjmp(brom_ctx, BROM_BOOT_NEXTSTAGE);
+}
+
+/*
+ * All Rockchip BROM implementations enter with a valid stack-pointer,
+ * so this can safely be implemented in C (providing a single
+ * implementation both for ARMv7 and AArch64).
+ */
+int save_boot_params(void)
+{
+	int  ret = setjmp(brom_ctx);
+
+	switch (ret) {
+	case 0:
+		/*
+		 * This is the initial pass through this function
+		 * (i.e. saving the context), setjmp just setup up the
+		 * brom_ctx: transfer back into the startup-code at
+		 * 'save_boot_params_ret' and let the compiler know
+		 * that this will not return.
+		 */
+		save_boot_params_ret();
+		while (true)
+			/* does not return */;
+		break;
+
+	case BROM_BOOT_NEXTSTAGE:
+		/*
+		 * To instruct the BROM to boot the next stage, we
+		 * need to return 0 to it: i.e. we need to rewrite
+		 * the return code once more.
+		 */
+		ret = 0;
+		break;
+
+	default:
+#if CONFIG_IS_ENABLED(LIBCOMMON_SUPPORT)
+		puts("FATAL: unexpected command to back_to_bootrom()\n");
+#endif
+		hang();
+	};
+
+	return ret;
 }

arch/arm/mach-rockchip/save_boot_param.S

@@ -1,69 +0,0 @@
-/*
- * (C) Copyright 2016 Rockchip Electronics Co., Ltd
- * (C) Copyright 2017 Theobroma Systems Design und Consulting GmbH
- *
- * SPDX-License-Identifier:     GPL-2.0+
- */
-
-#include <linux/linkage.h>
-
-#if defined(CONFIG_ARM64)
-.globl	SAVE_SP_ADDR
-SAVE_SP_ADDR:
-	.quad 0
-
-ENTRY(save_boot_params)
-	sub	sp, sp, #0x60
-	stp	x29, x30, [sp, #0x50]
-	stp	x27, x28, [sp, #0x40]
-	stp	x25, x26, [sp, #0x30]
-	stp	x23, x24, [sp, #0x20]
-	stp	x21, x22, [sp, #0x10]
-	stp	x19, x20, [sp, #0]
-	ldr	x8, =SAVE_SP_ADDR
-	mov	x9, sp
-	str	x9, [x8]
-	b	save_boot_params_ret  /* back to my caller */
-ENDPROC(save_boot_params)
-
-.globl _back_to_bootrom_s
-ENTRY(_back_to_bootrom_s)
-	ldr	x0, =SAVE_SP_ADDR
-	ldr	x0, [x0]
-	mov	sp, x0
-	ldp	x29, x30, [sp, #0x50]
-	ldp	x27, x28, [sp, #0x40]
-	ldp	x25, x26, [sp, #0x30]
-	ldp	x23, x24, [sp, #0x20]
-	ldp	x21, x22, [sp, #0x10]
-	ldp	x19, x20, [sp]
-	add	sp, sp, #0x60
-	mov	x0, xzr
-	ret
-ENDPROC(_back_to_bootrom_s)
-#else
-.globl	SAVE_SP_ADDR
-SAVE_SP_ADDR:
-	.word 0
-
-/*
- * void save_boot_params
- *
- * Save sp, lr, r1~r12
- */
-ENTRY(save_boot_params)
-	push	{r1-r12, lr}
-	ldr	r0, =SAVE_SP_ADDR
-	str	sp, [r0]
-	b	save_boot_params_ret		@ back to my caller
-ENDPROC(save_boot_params)
-
-
-.globl _back_to_bootrom_s
-ENTRY(_back_to_bootrom_s)
-	ldr	r0, =SAVE_SP_ADDR
-	ldr	sp, [r0]
-	mov	r0, #0
-	pop	{r1-r12, pc}
-ENDPROC(_back_to_bootrom_s)
-#endif