RISC-V: Support separate firmware and kernel payload

Support for separate firmware and kernel payload is added
by updating BBL to read optional preloaded kernel address
attributes from device-tree using a similar mechanism to
that used to pass init ramdisk addresses to linux kernel.

    chosen {
        riscv,kernel-start = <0x00000000 0x80200000>;
        riscv,kernel-end = <0x00000000 0x80590634>;
    };

These attributes are added by QEMU and read by BBL when combining
-bios <firmware-image> and -kernel <kernel-image> options. e.g.

$ qemu-system-riscv64 -machine virt -bios bbl -kernel vmlinux

With this change, bbl can be compiled without --with-payload
and the dummy payload alignment is altered to make the memory
footprint of the firmware-only bbl smaller. The dummy payload
message is updated to indicate the alternative load method.

This load method could also be supported by a first stage boot
loader that reads seperate firmware and kernel from SPI flash.
The main advantage of this new mechanism is that it eases kernel
development by avoiding the riscv-pk packaging step after kernel
builds, makes building per repository artefacts for CI simpler,
and mimics bootloaders on other platforms that can load a kernel
image file directly. Ultimately BBL should use an SPI driver to
load the kernel image however this mechanism supports use cases
such such as QEMU's -bios, -kernel and -initrd options following
examples from other platforms that pass kernel entry to firmware
via device-tree.

Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Alistair Francis <Alistair.Francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/configure b/configure
index 5af7cee..058eea1 100755
--- a/configure
+++ b/configure
@@ -4092,7 +4092,6 @@ case "${BUILD_32BIT}" in
 	CFLAGS="$default_CFLAGS"
 	LDFLAGS=
 	install_subdir=$host_alias
-
 	;;
 esac
 
@@ -4251,10 +4250,20 @@ fi
 
 # Check whether --with-payload was given.
 if test "${with_payload+set}" = set; then :
-  withval=$with_payload; BBL_PAYLOAD=$with_payload
+  withval=$with_payload;
+   BBL_PAYLOAD=$with_payload
+
+
+$as_echo "#define RELAXED_ALIGNMENT 0" >>confdefs.h
+
 
 else
-  BBL_PAYLOAD=dummy_payload
+
+   BBL_PAYLOAD=dummy_payload
+
+
+$as_echo "#define RELAXED_ALIGNMENT 1" >>confdefs.h
+
 
 fi