rpi4: Accommodate "armstub8.bin" header at the beginning of BL31 image
The Raspberry Pi GPU firmware checks for a magic value at offset 240
(0xf0) of the armstub8.bin image it loads. If that value matches,
it writes the kernel load address and the DTB address into subsequent
memory locations.
We can use these addresses to avoid hardcoding these values into the BL31
image, to make it more flexible and a drop-in replacement for the
official armstub8.bin.
Reserving just 16 bytes at offset 240 of the final image file is not easily
possible, though, as this location is in the middle of the generic BL31
entry point code.
However we can prepend an extra section before the actual BL31 image, to
contain the magic and addresses. This needs to be 4KB, because the
actual BL31 entry point needs to be page aligned.
Use the platform linker script hook that the generic code provides, to
add an almost empty 4KB code block before the entry point code. The very
first word contains a branch instruction to jump over this page, into
the actual entry code.
This also gives us plenty of room for the SMP pens later.
Change-Id: I38caa5e7195fa39cbef8600933a03d86f09263d6
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/rpi/rpi4/rpi4_bl31_setup.c b/plat/rpi/rpi4/rpi4_bl31_setup.c
index de582b3..58025b2 100644
--- a/plat/rpi/rpi4/rpi4_bl31_setup.c
+++ b/plat/rpi/rpi4/rpi4_bl31_setup.c
@@ -13,12 +13,21 @@
#include <lib/mmio.h>
#include <lib/xlat_tables/xlat_mmu_helpers.h>
#include <lib/xlat_tables/xlat_tables_defs.h>
+#include <lib/xlat_tables/xlat_tables_v2.h>
#include <plat/common/platform.h>
#include <drivers/arm/gicv2.h>
#include <rpi_shared.h>
+/*
+ * Fields at the beginning of armstub8.bin.
+ * While building the BL31 image, we put the stub magic into the binary.
+ * The GPU firmware detects this at boot time, clears that field as a
+ * confirmation and puts the kernel and DT address in the following words.
+ */
+extern uint32_t stub_magic;
+
static const gicv2_driver_data_t rpi4_gic_data = {
.gicd_base = RPI4_GIC_GICD_BASE,
.gicc_base = RPI4_GIC_GICC_BASE,
@@ -141,6 +150,14 @@
void bl31_plat_arch_setup(void)
{
+ /*
+ * Add the first page of memory, which holds the stub magic,
+ * the kernel and the DT address.
+ * This is read-only, as the GPU already populated the header,
+ * we just need to read it.
+ */
+ mmap_add_region(0, 0, 4096, MT_MEMORY | MT_RO | MT_SECURE);
+
rpi3_setup_page_tables(BL31_BASE, BL31_END - BL31_BASE,
BL_CODE_BASE, BL_CODE_END,
BL_RO_DATA_BASE, BL_RO_DATA_END