[PATCH v1 2/3] xen/riscv: add RISC-V legacy SBI extension support for guests

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

This commit adds support for legacy SBI extensions (version 0.1) in Xen
for guest domains.

The changes include:
1. Define all legacy SBI extension IDs (0x0 to 0x8) for better clarity and
   completeness.
2. Implement handling of legacy SBI extensions, starting with support for
   SBI_EXT_0_1_CONSOLE_{PUT,GET}CHAR.

The implementation uses the existing virtual SBI framework to handle legacy
SBI ecalls, ensuring compatibility with older SBI specifications in
RISC-V guests.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/arch/riscv/include/asm/sbi.h            | 11 ++++--
 xen/arch/riscv/vsbi/Makefile                |  1 +
 xen/arch/riscv/vsbi/vsbi-legacy-extension.c | 37 +++++++++++++++++++++
 3 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 xen/arch/riscv/vsbi/vsbi-legacy-extension.c

diff --git a/xen/arch/riscv/include/asm/sbi.h b/xen/arch/riscv/include/asm/sbi.h
index ade24a572d..e7d5d707b1 100644
--- a/xen/arch/riscv/include/asm/sbi.h
+++ b/xen/arch/riscv/include/asm/sbi.h
@@ -14,8 +14,15 @@
 
 #include <xen/cpumask.h>
 
-#define SBI_EXT_0_1_CONSOLE_PUTCHAR            0x1
-#define SBI_EXT_0_1_SHUTDOWN                   0x8
+#define SBI_EXT_0_1_SET_TIMER           0x0
+#define SBI_EXT_0_1_CONSOLE_PUTCHAR     0x1
+#define SBI_EXT_0_1_CONSOLE_GETCHAR     0x2
+#define SBI_EXT_0_1_CLEAR_IPI           0x3
+#define SBI_EXT_0_1_SEND_IPI            0x4
+#define SBI_EXT_0_1_REMOTE_FENCE_I      0x5
+#define SBI_EXT_0_1_REMOTE_SFENCE_VMA   0x6
+#define SBI_EXT_0_1_REMOTE_SFENCE_VMA_ASID  0x7
+#define SBI_EXT_0_1_SHUTDOWN            0x8
 
 #define SBI_EXT_BASE                    0x10
 #define SBI_EXT_RFENCE                  0x52464E43
diff --git a/xen/arch/riscv/vsbi/Makefile b/xen/arch/riscv/vsbi/Makefile
index 574c8ff78d..4da625db9a 100644
--- a/xen/arch/riscv/vsbi/Makefile
+++ b/xen/arch/riscv/vsbi/Makefile
@@ -1 +1,2 @@
 obj-y += vsbi.o
+obj-y += vsbi-legacy-extension.o
diff --git a/xen/arch/riscv/vsbi/vsbi-legacy-extension.c 
b/xen/arch/riscv/vsbi/vsbi-legacy-extension.c
new file mode 100644
index 0000000000..39d65931b1
--- /dev/null
+++ b/xen/arch/riscv/vsbi/vsbi-legacy-extension.c
@@ -0,0 +1,37 @@
+
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/lib.h>
+#include <xen/sched.h>
+
+#include <asm/processor.h>
+#include <asm/vsbi.h>
+
+static int vsbi_legacy_ecall_handler(struct vcpu *vcpu, unsigned long eid,
+                                     unsigned long fid,
+                                     struct cpu_user_regs *regs)
+{
+    int ret = 0;
+
+    switch ( eid )
+    {
+    case SBI_EXT_0_1_CONSOLE_PUTCHAR:
+        printk("%c", (char)regs->a0);
+        break;
+
+    case SBI_EXT_0_1_CONSOLE_GETCHAR:
+        regs->a0 = SBI_ERR_NOT_SUPPORTED;
+        break;
+
+    default:
+        panic("%s: Unsupported ecall: FID: #%lx, EID: #%lx\n",
+              __func__, fid, eid);
+               break;
+    }
+
+    return ret;
+}
+
+VSBI_EXT_START(legacy, SBI_EXT_0_1_SET_TIMER, SBI_EXT_0_1_SHUTDOWN,
+               vsbi_legacy_ecall_handler)
+VSBI_EXT_END
-- 
2.52.0