soc/cavium/bootblock: Get rid of register X1

The register X1 isn't used. Document it and remove it.

Change-Id: I9324ea9de24ba4baaef9dde890c443dd0f921ad9
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/23792
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>

src/soc/cavium/cn81xx/bootblock_custom.S

@@ -29,7 +29,11 @@ ENTRY(_start)
      */
     ic      ialluis
     fmov    d30, x0     /* Save X0 in FPR for use later */
-    fmov    d31, x1     /* Save X1 in FPR for use later */
+     /**
+      * The BDK stores X1 for later use, but it turns out that we don't need
+      * this "feature". The idea is to hide the devicetree somewhere in
+      * flash, that only the ROM will find it and point to it using X1.
+      */
     adr     x1, _start  /* x1 = _start location based on PC */
     fmov    d29, x1     /* Save PC in FPR for use later */
 
@@ -84,7 +88,7 @@ node_check_done:
     adr     x0, _start
 
     /**
-     * Check if IROM has loaded the code to CONFIG_BOOTROM_OFFSET.
+     * Check if IROM has loaded the code to BOOTROM_OFFSET.
      * In case the offset is wrong, try to relocate.
      * Ideally the following code is never executed.
      * FIXME: Add region overlap check.
@@ -248,8 +252,7 @@ ENTRY(start)
     bl      arm64_init_cpu
 
     fmov    x0, d30 /* The original X0, info from previous image */
-    fmov    x1, d31 /* The original X1, info from previous image */
-    fmov    x2, d29 /* The original PC we were loaded at */
+    fmov    x1, d29 /* The original PC we were loaded at */
 
     /* Call C entry */
     bl      bootblock_main

src/soc/cavium/common/bootblock.c

@@ -32,7 +32,6 @@ __attribute__((weak)) void bootblock_mainboard_init(void) { /* do nothing */ }
 
 /* C code entry point for the boot block */
 void bootblock_main(const uint64_t reg_x0,
-		    const uint64_t reg_x1,
 		    const uint64_t reg_pc)
 {
 	uint64_t base_timestamp = 0;
@@ -57,8 +56,6 @@ void bootblock_main(const uint64_t reg_x0,
 			printk(BIOS_ERR,
 			       "BOOTBLOCK: RST Boot Failure Code %lld\n",
 			       reg_x0);
-
-		printk(BIOS_DEBUG, "BOOTBLOCK: FDT 0x%llX\n", reg_x1);
 	}
 
 	bootblock_soc_init();

src/soc/cavium/common/include/soc/bootblock.h

@@ -22,7 +22,6 @@ void bootblock_soc_init(void);
 void bootblock_mainboard_init(void);
 
 void bootblock_main(const uint64_t reg_x0,
-		    const uint64_t reg_x1,
 		    const uint64_t reg_pc);