rk27xx: support entering rkusb mode on rk2706A

We know about two different bootroms. First can be found in rk2706A,
the second in rk2706B and rk2705. This two versions are very
similar but memory addresses are different. It seems it is possible
to distinguish bootrom version by reading SCU_ID register.

Change-Id: I01681b5e3a82930ae74a5cce6ab0244d7cd333d2

1 files changed, 36 insertions, 9 deletions

diff --git a/bootloader/rk27xx.c b/bootloader/rk27xx.c
index 62280e2749..bcf1f8f764 100644
--- a/bootloader/rk27xx.c
+++ b/bootloader/rk27xx.c
@@ -37,42 +37,69 @@ extern void show_logo( void );
 static void enter_rkusb(void)
 {
     asm volatile (
-        /* turn off cache */
+        /* Turn off cache */
         "ldr     r0, =0xefff0000 \n"
         "ldrh    r1, [r0] \n"
         "strh    r1, [r0] \n"
 
-        /* turn off interrupts */
+        /* Turn off interrupts */
         "mrs     r0, cpsr \n"
         "bic     r0, r0, #0x1f \n"
         "orr     r0, r0, #0xd3 \n"
         "msr     cpsr, r0 \n"
 
-        /* disable iram remap */
+        /* Disable iram remap */
         "mov     r0, #0x18000000 \n"
         "add     r0, r0, #0x1c000 \n"
         "mov     r1, #0 \n"
         "str     r1, [r0, #4] \n"
 
-        /* setup stacks in unmapped
-         * iram just as rom will do
+        /* Ungate all clocks */
+        "str     r1, [r0, #0x18] \n"
+
+        /* Read SCU_ID to determine
+         * which version of bootrom we have
+         * 2706A has ID 0xa1000604
+         * 2706B and 2705 have ID 0xa10002b7
          */
-        "msr     cpsr, #0xd2 \n"
+        "ldr     r1, [r0] \n"
+        "ldr     r2, =0xa1000604 \n"
+        "cmp     r1, r2 \n"
+        "bne     rk27xx_new \n"
+
+        /* Setup stacks in unmapped
+         * iram just as rom will do.
+         *
+         * We know about two versions
+         * of bootrom which are very similar
+         * but memory addresses are slightly
+         * different.
+         */
+        "rk27xx_old: \n"
+        "ldr     r1, =0x18200258 \n"
+        "ldr     r0, =0xaf0 \n"
+        "b       jump_to_rom \n"
+
+        "rk27xx_new: \n"
         "ldr     r1, =0x18200274 \n"
+        "ldr     r0, =0xec0 \n"
+
+        "jump_to_rom: \n"
+        "msr     cpsr, #0xd2 \n"
         "add     r1, r1, #0x200 \n"
         "mov     sp, r1 \n"
         "msr     cpsr, #0xd3 \n"
         "add     r1, r1, #0x400 \n"
         "mov     sp, r1 \n"
 
-        /* jump to main() in rom
-         * just before dfu handler
+        /* Finaly jump to rkusb handler
+         * in bootrom.
          */
-        "ldr     r0, =0xec0 \n"
         "bx      r0 \n"
     );
 }
 
+
 void main(void) NORETURN_ATTR;
 void main(void)
 {