[PATCH v2] target/riscv: Implement optional CSR mcontext of debug Sdtrig extension

[Alvin Chang]

The debug Sdtrig extension defines an CSR "mcontext". This commit
implements its predicate and read/write operations into CSR table.
Its value is reset as 0 when the trigger module is reset.

Signed-off-by: Alvin Chang <alvinga@andestech.com>
---
Changes from v1: Remove dedicated cfg, always implement mcontext.

 target/riscv/cpu.h      |  1 +
 target/riscv/cpu_bits.h |  7 +++++++
 target/riscv/csr.c      | 36 +++++++++++++++++++++++++++++++-----
 target/riscv/debug.c    |  2 ++
 4 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index d74b361..e117641 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -345,6 +345,7 @@ struct CPUArchState {
     target_ulong tdata1[RV_MAX_TRIGGERS];
     target_ulong tdata2[RV_MAX_TRIGGERS];
     target_ulong tdata3[RV_MAX_TRIGGERS];
+    target_ulong mcontext;
     struct CPUBreakpoint *cpu_breakpoint[RV_MAX_TRIGGERS];
     struct CPUWatchpoint *cpu_watchpoint[RV_MAX_TRIGGERS];
     QEMUTimer *itrigger_timer[RV_MAX_TRIGGERS];
diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
index ebd7917..3296648 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -361,6 +361,7 @@
 #define CSR_TDATA2          0x7a2
 #define CSR_TDATA3          0x7a3
 #define CSR_TINFO           0x7a4
+#define CSR_MCONTEXT        0x7a8
 
 /* Debug Mode Registers */
 #define CSR_DCSR            0x7b0
@@ -905,4 +906,10 @@ typedef enum RISCVException {
 /* JVT CSR bits */
 #define JVT_MODE                           0x3F
 #define JVT_BASE                           (~0x3F)
+
+/* Debug Sdtrig CSR masks */
+#define MCONTEXT32                         0x0000003F
+#define MCONTEXT64                         0x0000000000001FFFULL
+#define MCONTEXT32_HCONTEXT                0x0000007F
+#define MCONTEXT64_HCONTEXT                0x0000000000003FFFULL
 #endif
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index fde7ce1..ff1e128 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3900,6 +3900,31 @@ static RISCVException read_tinfo(CPURISCVState *env, int 
csrno,
     return RISCV_EXCP_NONE;
 }
 
+static RISCVException read_mcontext(CPURISCVState *env, int csrno,
+                                    target_ulong *val)
+{
+    *val = env->mcontext;
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException write_mcontext(CPURISCVState *env, int csrno,
+                                     target_ulong val)
+{
+    bool rv32 = riscv_cpu_mxl(env) == MXL_RV32 ? true : false;
+    int32_t mask;
+
+    if (riscv_has_ext(env, RVH)) {
+        /* Spec suggest 7-bit for RV32 and 14-bit for RV64 w/ H extension */
+        mask = rv32 ? MCONTEXT32_HCONTEXT : MCONTEXT64_HCONTEXT;
+    } else {
+        /* Spec suggest 6-bit for RV32 and 13-bit for RV64 w/o H extension */
+        mask = rv32 ? MCONTEXT32 : MCONTEXT64;
+    }
+
+    env->mcontext = val & mask;
+    return RISCV_EXCP_NONE;
+}
+
 /*
  * Functions to access Pointer Masking feature registers
  * We have to check if current priv lvl could modify
@@ -4794,11 +4819,12 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     [CSR_PMPADDR15] =  { "pmpaddr15", pmp, read_pmpaddr, write_pmpaddr },
 
     /* Debug CSRs */
-    [CSR_TSELECT]   =  { "tselect", debug, read_tselect, write_tselect },
-    [CSR_TDATA1]    =  { "tdata1",  debug, read_tdata,   write_tdata   },
-    [CSR_TDATA2]    =  { "tdata2",  debug, read_tdata,   write_tdata   },
-    [CSR_TDATA3]    =  { "tdata3",  debug, read_tdata,   write_tdata   },
-    [CSR_TINFO]     =  { "tinfo",   debug, read_tinfo,   write_ignore  },
+    [CSR_TSELECT]   =  { "tselect",  debug, read_tselect,  write_tselect  },
+    [CSR_TDATA1]    =  { "tdata1",   debug, read_tdata,    write_tdata    },
+    [CSR_TDATA2]    =  { "tdata2",   debug, read_tdata,    write_tdata    },
+    [CSR_TDATA3]    =  { "tdata3",   debug, read_tdata,    write_tdata    },
+    [CSR_TINFO]     =  { "tinfo",    debug, read_tinfo,    write_ignore   },
+    [CSR_MCONTEXT]  =  { "mcontext", debug, read_mcontext, write_mcontext },
 
     /* User Pointer Masking */
     [CSR_UMTE]    =    { "umte",    pointer_masking, read_umte,  write_umte },
diff --git a/target/riscv/debug.c b/target/riscv/debug.c
index 4945d1a..e30d99c 100644
--- a/target/riscv/debug.c
+++ b/target/riscv/debug.c
@@ -940,4 +940,6 @@ void riscv_trigger_reset_hold(CPURISCVState *env)
         env->cpu_watchpoint[i] = NULL;
         timer_del(env->itrigger_timer[i]);
     }
+
+    env->mcontext = 0;
 }
-- 
2.34.1