[PATCH v2] hw/riscv: virt: Assume M-mode FW in pflash0 only when "-bios none"

[Sunil V L]

Currently, virt machine supports two pflash instances each with
32MB size. However, the first pflash is always assumed to
contain M-mode firmware and reset vector is set to this if
enabled. Hence, for S-mode payloads like EDK2, only one pflash
instance is available for use. This means both code and NV variables
of EDK2 will need to use the same pflash.

The OS distros keep the EDK2 FW code as readonly. When non-volatile
variables also need to share the same pflash, it is not possible
to keep it as readonly since variables need write access.

To resolve this issue, the code and NV variables need to be separated.
But in that case we need an extra flash. Hence, modify the convention
such that pflash0 will contain the M-mode FW only when "-bios none"
option is used. Otherwise, pflash0 will contain the S-mode payload FW.
This enables both pflash instances available for EDK2 use.

Example usage:
1) pflash0 containing M-mode FW
qemu-system-riscv64 -bios none -pflash <mmode_fw> -machine virt
or
qemu-system-riscv64 -bios none \
-drive file=<mmode_fw>,if=pflash,format=raw,unit=0 -machine virt

2) pflash0 containing S-mode payload like EDK2
qemu-system-riscv64 -pflash <smode_fw_vars> -pflash <smode_fw_code> -machine  
virt
or
qemu-system-riscv64 -bios <opensbi_fw> \
-pflash <smode_fw_vars> \
-pflash <smode_fw_code> \
-machine  virt
or
qemu-system-riscv64 -bios <opensbi_fw> \
-drive file=<smode_fw_vars>,if=pflash,format=raw,unit=0 \
-drive file=<smode_fw_code>,if=pflash,format=raw,unit=1,readonly=on  \
-machine virt

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
---
The issue is reported at
https://salsa.debian.org/qemu-team/edk2/-/commit/c345655a0149f64c5020bfc1e53c619ce60587f6

The patch is based on Alistair's riscv-to-apply.next branch.

Changes since v1:
        1) Simplified the fix such that it doesn't break current EDK2.

 hw/riscv/virt.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index 4e3efbee16..ca445d3d02 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -1296,10 +1296,11 @@ static void virt_machine_done(Notifier *notifier, void 
*data)
         kernel_entry = 0;
     }
 
-    if (drive_get(IF_PFLASH, 0, 0)) {
+    if (drive_get(IF_PFLASH, 0, 0) &&
+                 machine->firmware && !strcmp(machine->firmware, "none")) {
         /*
-         * Pflash was supplied, let's overwrite the address we jump to after
-         * reset to the base of the flash.
+         * Pflash0 was supplied with "-bios none", let's overwrite the address
+         * we jump to after reset to the base of the flash.
          */
         start_addr = virt_memmap[VIRT_FLASH].base;
     }
-- 
2.34.1