core: arm: S-EL1 SPMC: boot ABI update

Updates the boot ABI for S-EL1 SPMC to align better with other SPMCs,
like Hafnium, but also with the non-FF-A configuration.

Register usage:
X0 - TOS FW config [1] address, if not NULL
X2 - System DTB, if not NULL

Adds check in the default get_aslr_seed() to see if the system DTB is
present before trying to read kaslr-seed from secure-chosen.

Note that this is an incompatible change and requires corresponding
change in TF-A ("feat(qemu): update abi between spmd and spmc") [2].

[1] A TF-A concept: TOS_FW_CONFIG - Trusted OS Firmware configuration
    file. Used by Trusted OS (BL32), that is, OP-TEE in this case
Link: [2] https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/commit/?id=25ae7ad1878244f78206cc7c91f7bdbd267331a1

Acked-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

core/arch/arm/kernel/boot.c

@@ -1502,11 +1502,17 @@ struct ns_entry_context *boot_core_hpen(void)
 #if defined(CFG_DT)
 unsigned long __weak get_aslr_seed(void *fdt)
 {
-	int rc = fdt_check_header(fdt);
+	int rc = 0;
 	const uint64_t *seed = NULL;
 	int offs = 0;
 	int len = 0;
 
+	if (!fdt) {
+		DMSG("No fdt");
+		goto err;
+	}
+
+	rc = fdt_check_header(fdt);
 	if (rc) {
 		DMSG("Bad fdt: %d", rc);
 		goto err;

core/arch/arm/kernel/entry_a64.S

@@ -143,21 +143,20 @@
 	.endm
 
 FUNC _start , :
-#if defined(CFG_CORE_SEL1_SPMC)
 	/*
-	 * With OP-TEE as SPMC at S-EL1 the SPMD (SPD_spmd) in TF-A passes
-	 * the DTB in x0, pagaeble part in x1 and the rest of the registers
-	 * are unused
+	 * If CFG_CORE_FFA is enabled, then x0 if non-NULL holds the TOS FW
+	 * config [1] address, else x0 if non-NULL holds the pagable part
+	 * address.
+	 *
+	 * [1] A TF-A concept: TOS_FW_CONFIG - Trusted OS Firmware
+	 * configuration file. Used by Trusted OS (BL32), that is, OP-TEE
+	 * here.
 	 */
-	mov	x19, x1		/* Save pagable part */
-	mov	x20, x0		/* Save DT address */
-#else
-	mov	x19, x0		/* Save pagable part address */
+	mov	x19, x0
 #if defined(CFG_DT_ADDR)
 	ldr     x20, =CFG_DT_ADDR
 #else
 	mov	x20, x2		/* Save DT address */
-#endif
 #endif
 
 	adr	x0, reset_vect_table