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>
Series-cc: Andy Yan <andy.yan@rock-chips.com>
Series-cc: Klaus Goger <klaus.goger@theobroma-systems.com>

Series-version: 3

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

Recent discussions confirmed (what the code always assumed): the
Rockchip BROM always enters U-Boot with the stack-pointer valid
(i.e. the U-Boot startup code is running off the BROM stack).

We can thus replace the back-to-bootrom code (i.e. both the
save_boot_params and back_to_bootrom implementations) using C-code
based on setjmp/longjmp.  The new implementation is already structured
to allow an easy drop-in of Andy's changes to enter download-mode when
returning to the BROM.

This turned out to require a some tweaking to system.h (making sure
that the prototype for save_boot_params_ret is visible for A64)and
start.S (so binutils knows that this is a possible function entry and
it can correctly insert A32-to-Thumb transitions) and taking the axe
to setjmp.h (which created quite a few issues with it not expecting
A32/T32/Thumb call-sites and some fragility from GCC being smart about
the clobber-list of the inline assembly... which led to r9 not being
saved or restored).
END

1 files changed, 51 insertions, 1 deletions

diff --git a/arch/arm/mach-rockchip/bootrom.c b/arch/arm/mach-rockchip/bootrom.c
index 8380e4e006..7b9b307a89 100644
--- a/arch/arm/mach-rockchip/bootrom.c
+++ b/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;
 }