riscv: qemu: detect and boot the kernel passed by QEMU

QEMU embeds the location of the kernel image in the device tree. Store
this address in the environment as variable kernel_start and use it in
CONFIG_BOOTCOMMAND to boot the kernel.

Signed-off-by: Lukas Auer <[email protected]>
Series-to: u-boot
Series-cc: bmeng
Cover-letter:
General fixes / cleanup for RISC-V and improvements to qemu-riscv

This patch series includes general fixes and cleanup for RISC-V. It also
adds support for booting Linux on qemu-riscv. At the moment, only
single-core systems are supported. Support for multi-core systems will
be added with a future patch series.

To boot Linux on qemu-riscv, Linux must be compiled into BBL as a
payload. BBL must be included in a FIT image and supplied to QEMU with
the -kernel parameter. Its location in memory is embedded in the device
tree, which QEMU passes to u-boot.
To test this, QEMU and riscv-pk (BBL) must be modified. QEMU is modified
to add support for loading binary files (FIT images in this case) in
addition to ELF files. riscv-pk must be modified to adjust the link
address and to ignore the kernel address from the device tree. A pull
request for QEMU, which implements this, is available at [1]. A modified
version of riscv-pk is available at [2].

[1]: riscvarchive/riscv-qemu#175
[2]: https://github.com/lukasauer/riscv-pk/tree/riscv-u-boot
END

board/emulation/qemu-riscv/Kconfig

@@ -18,5 +18,6 @@ config SYS_TEXT_BASE
 config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
 	imply SYS_NS16550
+	imply BOARD_LATE_INIT
 
 endif

board/emulation/qemu-riscv/qemu-riscv.c

@@ -4,9 +4,39 @@
  */
 
 #include <common.h>
+#include <dm.h>
 #include <fdtdec.h>
 
 int board_init(void)
 {
 	return 0;
 }
+
+int board_late_init(void)
+{
+	ulong kernel_start;
+	ofnode chosen_node;
+	int ret;
+
+	chosen_node = ofnode_path("/chosen");
+	if (!ofnode_valid(chosen_node)) {
+		printf("No chosen node found\n");
+		return 0;
+	}
+
+#ifdef CONFIG_ARCH_RV64I
+	ret = ofnode_read_u64(chosen_node, "riscv,kernel-start",
+			      (u64 *)&kernel_start);
+#else
+	ret = ofnode_read_u32(chosen_node, "riscv,kernel-start",
+			      (u32 *)&kernel_start);
+#endif
+	if (ret) {
+		printf("Can't find kernel start address in device tree\n");
+		return 0;
+	}
+
+	env_set_hex("kernel_start", kernel_start);
+
+	return 0;
+}

configs/qemu-riscv32_defconfig

@@ -4,4 +4,5 @@ CONFIG_NR_DRAM_BANKS=1
 CONFIG_FIT=y
 CONFIG_DISPLAY_CPUINFO=y
 CONFIG_DISPLAY_BOARDINFO=y
+CONFIG_HUSH_PARSER=y
 CONFIG_OF_PRIOR_STAGE=y

configs/qemu-riscv64_defconfig

@@ -5,4 +5,5 @@ CONFIG_NR_DRAM_BANKS=1
 CONFIG_FIT=y
 CONFIG_DISPLAY_CPUINFO=y
 CONFIG_DISPLAY_BOARDINFO=y
+CONFIG_HUSH_PARSER=y
 CONFIG_OF_PRIOR_STAGE=y

include/configs/qemu-riscv.h

@@ -24,4 +24,11 @@
 	"fdt_high=0xffffffffffffffff\0" \
 	"initrd_high=0xffffffffffffffff\0"
 
+#define CONFIG_BOOTCOMMAND \
+	"if env exists kernel_start; then " \
+		"bootm ${kernel_start};" \
+	"else " \
+		"echo Kernel address not found in the device tree;" \
+	"fi;"
+
 #endif /* __CONFIG_H */