arch/arm: Add support for loading Linux kernels

Adds support for loading Linux kernels through FIT payloads. This has
been implemented as an assembly function in order to simplify dealing
with some of the intricacies of loading a kernel (such as needing to
jump to the kernel in ARM mode and the kernel ABI).

TEST: Booted a FIT image containing a 5.4 kernel and initramfs on the
Beaglebone Black.

Change-Id: I7dbf9467665ec17447cec73676763844b4be4764
Signed-off-by: Sam Lewis <sam.vr.lewis@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45335
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

1 files changed, 20 insertions, 2 deletions

diff --git a/src/arch/arm/boot.c b/src/arch/arm/boot.c
index 8c876de0b0..b18473b924 100644
--- a/src/arch/arm/boot.c
+++ b/src/arch/arm/boot.c
@@ -1,14 +1,32 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <cbfs.h>
 #include <arch/cache.h>
 #include <program_loading.h>
 
+void boot_linux(void *kernel_ptr, void *fdt_ptr);
+
 void arch_prog_run(struct prog *prog)
 {
 	void (*doit)(void *);
 
 	cache_sync_instructions();
 
-	doit = prog_entry(prog);
-	doit(prog_entry_arg(prog));
+	switch (prog_cbfs_type(prog)) {
+	case CBFS_TYPE_FIT:
+		/*
+		 * We only load Linux payloads from the ramstage, so provide a hint to
+		 * the linker that the below functions do not need to be included in
+		 * earlier stages.
+		 */
+		if (!ENV_RAMSTAGE)
+			break;
+
+		dcache_mmu_disable();
+		boot_linux(prog_entry(prog), prog_entry_arg(prog));
+		break;
+	default:
+		doit = prog_entry(prog);
+		doit(prog_entry_arg(prog));
+	}
 }