hw/riscv: Load OpenSBI as the default firmware

If the user hasn't specified a firmware to load (with -bios) or
specified no bios (with -bios none) then load OpenSBI by default. This
allows users to boot a RISC-V kernel with just -kernel.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

hw/riscv/boot.c

@@ -18,6 +18,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu-common.h"
 #include "qemu/units.h"
 #include "qemu/error-report.h"
 #include "exec/cpu-defs.h"
@@ -32,6 +33,59 @@
 # define KERNEL_BOOT_ADDRESS 0x80200000
 #endif
 
+void riscv_find_and_load_firmware(MachineState *machine,
+                                  const char *default_machine_firmware,
+                                  hwaddr firmware_load_addr)
+{
+    char *firmware_filename;
+
+    if (!machine->firmware) {
+        /*
+         * The user didn't specify -bios.
+         * At the moment we default to loading nothing when this hapens.
+         * In the future this defaul will change to loading the prebuilt
+         * OpenSBI firmware. Let's warn the user and then continue.
+        */
+        warn_report("No -bios option specified. Not loading a firmware.");
+        warn_report("This default will change in QEMU 4.3. Please use the " \
+                    "-bios option to aviod breakages when this happens.");
+        warn_report("See QEMU's deprecation documentation for details");
+        return;
+    }
+
+    if (!strcmp(machine->firmware, "default")) {
+        /*
+         * The user has specified "-bios default". That means we are going to
+         * load the OpenSBI binary included in the QEMU source.
+         *
+         * We can't load the binary by default as it will break existing users
+         * as users are already loading their own firmware.
+         *
+         * Let's try to get everyone to specify the -bios option at all times,
+         * so then in the future we can make "-bios default" the default option
+         * if no -bios option is set without breaking anything.
+         */
+        firmware_filename = qemu_find_file(QEMU_FILE_TYPE_BIOS,
+                                           default_machine_firmware);
+        if (firmware_filename == NULL) {
+            error_report("Unable to load the default RISC-V firmware \"%s\"",
+                         default_machine_firmware);
+            exit(1);
+        }
+    } else {
+        firmware_filename = machine->firmware;
+    }
+
+    if (strcmp(firmware_filename, "none")) {
+        /* If not "none" load the firmware */
+        riscv_load_firmware(firmware_filename, firmware_load_addr);
+    }
+
+    if (!strcmp(machine->firmware, "default")) {
+        g_free(firmware_filename);
+    }
+}
+
 target_ulong riscv_load_firmware(const char *firmware_filename,
                                  hwaddr firmware_load_addr)
 {

hw/riscv/sifive_u.c

@@ -49,6 +49,8 @@
 
 #include <libfdt.h>
 
+#define BIOS_FILENAME "opensbi-riscv64-sifive_u-fw_jump.bin"
+
 static const struct MemmapEntry {
     hwaddr base;
     hwaddr size;
@@ -269,9 +271,8 @@ static void riscv_sifive_u_init(MachineState *machine)
     /* create device tree */
     create_fdt(s, memmap, machine->ram_size, machine->kernel_cmdline);
 
-    if (machine->firmware) {
-        riscv_load_firmware(machine->firmware, memmap[SIFIVE_U_DRAM].base);
-    }
+    riscv_find_and_load_firmware(machine, BIOS_FILENAME,
+                                 memmap[SIFIVE_U_DRAM].base);
 
     if (machine->kernel_filename) {
         riscv_load_kernel(machine->kernel_filename);

hw/riscv/virt.c

@@ -44,6 +44,12 @@
 
 #include <libfdt.h>
 
+#if defined(TARGET_RISCV32)
+# define BIOS_FILENAME "opensbi-riscv32-virt-fw_jump.bin"
+#else
+# define BIOS_FILENAME "opensbi-riscv64-virt-fw_jump.bin"
+#endif
+
 static const struct MemmapEntry {
     hwaddr base;
     hwaddr size;
@@ -399,9 +405,8 @@ static void riscv_virt_board_init(MachineState *machine)
     memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
                                 mask_rom);
 
-    if (machine->firmware) {
-        riscv_load_firmware(machine->firmware, memmap[VIRT_DRAM].base);
-    }
+    riscv_find_and_load_firmware(machine, BIOS_FILENAME,
+                                 memmap[VIRT_DRAM].base);
 
     if (machine->kernel_filename) {
         uint64_t kernel_entry = riscv_load_kernel(machine->kernel_filename);

include/hw/riscv/boot.h

@@ -20,6 +20,9 @@
 #ifndef RISCV_BOOT_H
 #define RISCV_BOOT_H
 
+void riscv_find_and_load_firmware(MachineState *machine,
+                                  const char *default_machine_firmware,
+                                  hwaddr firmware_load_addr);
 target_ulong riscv_load_firmware(const char *firmware_filename,
                                  hwaddr firmware_load_addr);
 target_ulong riscv_load_kernel(const char *kernel_filename);

qemu-deprecated.texi

@@ -121,6 +121,26 @@ the backing storage specified with @option{-mem-path} can actually provide
 the guest RAM configured with @option{-m} and QEMU will fail to start up if
 RAM allocation is unsuccessful.
 
+@subsection RISC-V -bios (since 4.1)
+
+QEMU 4.1 introduced support for the -bios option in QEMU for RISC-V for the
+RISC-V virt machine and sifive_u machine.
+
+QEMU 4.1 has no changes to the default behaviour to avoid breakages. This
+default will change in a future QEMU release, so please prepare now. All users
+of the virt or sifive_u machine must change their command line usage.
+
+QEMU 4.1 has three options, please migrate to one of these three:
+ 1. ``-bios none`` - This is the current default behavior if no -bios option
+      is included. QEMU will not automatically load any firmware. It is up
+      to the user to load all the images they need.
+ 2. ``-bios default`` - In a future QEMU release this will become the default
+      behaviour if no -bios option is specified. This option will load the
+      default OpenSBI firmware automatically. The firmware is included with
+      the QEMU release and no user interaction is required. All a user needs
+      to do is specify the kernel they want to boot with the -kernel option
+ 3. ``-bios <file>`` - Tells QEMU to load the specified file as the firmwrae.
+
 @section QEMU Machine Protocol (QMP) commands
 
 @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0)