arm: mvebu: Add documentation for save_boot_params() function

Important detail is availability of kwbimage BIN header arguments passed
via r0 and r1 registers by BootROM.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>

diff --git a/arch/arm/mach-mvebu/lowlevel_spl.S b/arch/arm/mach-mvebu/lowlevel_spl.S
index dde77b765214dac504d68fec25d77453a4cd8161..501c239e9d38baa05579d05e8f7ccf0ad065997b 100644 (file)
--- a/arch/arm/mach-mvebu/lowlevel_spl.S
+++ b/arch/arm/mach-mvebu/lowlevel_spl.S
@@ -3,6 +3,15 @@
 #include <config.h>
 #include <linux/linkage.h>
 
+/*
+ * BootROM loads the header part of kwbimage into L2 cache. BIN header usually
+ * contains U-Boot SPL, optionally it can also contain additional arguments.
+ * The number of these arguments is in r0, pointer to the argument array in r1.
+ * BootROM expects executable BIN header code to return to address stored in lr.
+ * Other registers (r2 - r12) must be preserved. We save all registers to
+ * CONFIG_SPL_BOOTROM_SAVE address. BIN header arguments (passed via r0 and r1)
+ * are currently not used by U-Boot SPL binary.
+ */
 ENTRY(save_boot_params)
        stmfd   sp!, {r0 - r12, lr}     /* @ save registers on stack */
        ldr     r12, =CONFIG_SPL_BOOTROM_SAVE