Use the OnOffAuto type as 3-state.

Since the TCGState instance is zero-initialized, the
mttcg_enabled is initialzed as AUTO (ON_OFF_AUTO_AUTO).

In tcg_init_machine(), if mttcg_enabled is still AUTO,
set a default value (effectively inlining the
default_mttcg_enabled() method content).

Instead of emiting a warning when the 'thread' property
is set in tcg_set_thread(), emit it in tcg_init_machine()
where it is consumed. This is in preparation of the
next commit where we replace the TARGET_SUPPORTS_MTTCG
definition by getting the value at runtime via
CPUState -> CPUClass -> TCGCPUOps -> mttcg_supported,
so we need an initialized CPUState -- which is not
possible at instance_init time).

In the tcg_get_thread() getter, consider AUTO / OFF states
as "single", otherwise ON is "multi".

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Anton Johansson <anjo@rev.ng>
---
 accel/tcg/tcg-all.c | 69 ++++++++++++++++++++++-----------------------
 1 file changed, 34 insertions(+), 35 deletions(-)

diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index d75ecf531b6..f83f9b9d79e 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -32,6 +32,7 @@
 #include "qemu/error-report.h"
 #include "qemu/accel.h"
 #include "qemu/atomic.h"
+#include "qapi/qapi-types-common.h"
 #include "qapi/qapi-builtin-visit.h"
 #include "qemu/units.h"
 #if defined(CONFIG_USER_ONLY)
@@ -47,7 +48,7 @@
 struct TCGState {
     AccelState parent_obj;
 
-    bool mttcg_enabled;
+    OnOffAuto mttcg_enabled;
     bool one_insn_per_tb;
     int splitwx_enabled;
     unsigned long tb_size;
@@ -68,37 +69,10 @@ bool qemu_tcg_mttcg_enabled(void)
 }
 #endif
 
-/*
- * We default to false if we know other options have been enabled
- * which are currently incompatible with MTTCG. Otherwise when each
- * guest (target) has been updated to support:
- *   - atomic instructions
- *   - memory ordering primitives (barriers)
- * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
- *
- * Once a guest architecture has been converted to the new primitives
- * there is one remaining limitation to check:
- *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
- */
-
-static bool default_mttcg_enabled(void)
-{
-    if (icount_enabled()) {
-        return false;
-    }
-#ifdef TARGET_SUPPORTS_MTTCG
-    return true;
-#else
-    return false;
-#endif
-}
-
 static void tcg_accel_instance_init(Object *obj)
 {
     TCGState *s = TCG_STATE(obj);
 
-    s->mttcg_enabled = default_mttcg_enabled();
-
     /* If debugging enabled, default "auto on", otherwise off. */
 #if defined(CONFIG_DEBUG_TCG) && !defined(CONFIG_USER_ONLY)
     s->splitwx_enabled = -1;
@@ -117,8 +91,37 @@ static int tcg_init_machine(MachineState *ms)
 #else
     unsigned max_cpus = ms->smp.max_cpus;
 #endif
+#ifdef TARGET_SUPPORTS_MTTCG
+    bool mttcg_supported = true;
+#else
+    bool mttcg_supported = false;
+#endif
 
     tcg_allowed = true;
+
+    if (s->mttcg_enabled == ON_OFF_AUTO_AUTO) {
+        /*
+         * We default to false if we know other options have been enabled
+         * which are currently incompatible with MTTCG. Otherwise when each
+         * guest (target) has been updated to support:
+         *   - atomic instructions
+         *   - memory ordering primitives (barriers)
+         * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
+         *
+         * Once a guest architecture has been converted to the new primitives
+         * there is one remaining limitation to check:
+         *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
+         */
+        if (icount_enabled()) {
+            s->mttcg_enabled = ON_OFF_AUTO_OFF;
+        } else {
+            s->mttcg_enabled = mttcg_supported;
+        }
+    }
+    if (s->mttcg_enabled == ON_OFF_AUTO_ON && !mttcg_supported) {
+        warn_report("Guest not yet converted to MTTCG - "
+                    "you may get unexpected results");
+    }
     mttcg_enabled = s->mttcg_enabled;
 
     page_init();
@@ -144,7 +147,7 @@ static char *tcg_get_thread(Object *obj, Error **errp)
 {
     TCGState *s = TCG_STATE(obj);
 
-    return g_strdup(s->mttcg_enabled ? "multi" : "single");
+    return g_strdup(s->mttcg_enabled == ON_OFF_AUTO_ON ? "multi" : "single");
 }
 
 static void tcg_set_thread(Object *obj, const char *value, Error **errp)
@@ -155,14 +158,10 @@ static void tcg_set_thread(Object *obj, const char *value, Error **errp)
         if (icount_enabled()) {
             error_setg(errp, "No MTTCG when icount is enabled");
         } else {
-#ifndef TARGET_SUPPORTS_MTTCG
-            warn_report("Guest not yet converted to MTTCG - "
-                        "you may get unexpected results");
-#endif
-            s->mttcg_enabled = true;
+            s->mttcg_enabled = ON_OFF_AUTO_ON;
         }
     } else if (strcmp(value, "single") == 0) {
-        s->mttcg_enabled = false;
+        s->mttcg_enabled = ON_OFF_AUTO_OFF;
     } else {
         error_setg(errp, "Invalid 'thread' setting %s", value);
     }
-- 
2.47.1

On 3/21/25 11:34, Philippe Mathieu-Daudé wrote:
> Use the OnOffAuto type as 3-state.
> 
> Since the TCGState instance is zero-initialized, the
> mttcg_enabled is initialzed as AUTO (ON_OFF_AUTO_AUTO).
> 
> In tcg_init_machine(), if mttcg_enabled is still AUTO,
> set a default value (effectively inlining the
> default_mttcg_enabled() method content).
> 
> Instead of emiting a warning when the 'thread' property
> is set in tcg_set_thread(), emit it in tcg_init_machine()
> where it is consumed. This is in preparation of the
> next commit where we replace the TARGET_SUPPORTS_MTTCG
> definition by getting the value at runtime via
> CPUState -> CPUClass -> TCGCPUOps -> mttcg_supported,
> so we need an initialized CPUState -- which is not
> possible at instance_init time).
> 
> In the tcg_get_thread() getter, consider AUTO / OFF states
> as "single", otherwise ON is "multi".
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Reviewed-by: Anton Johansson <anjo@rev.ng>
> ---
>   accel/tcg/tcg-all.c | 69 ++++++++++++++++++++++-----------------------
>   1 file changed, 34 insertions(+), 35 deletions(-)
> 
> diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
> index d75ecf531b6..f83f9b9d79e 100644
> --- a/accel/tcg/tcg-all.c
> +++ b/accel/tcg/tcg-all.c
> @@ -32,6 +32,7 @@
>   #include "qemu/error-report.h"
>   #include "qemu/accel.h"
>   #include "qemu/atomic.h"
> +#include "qapi/qapi-types-common.h"
>   #include "qapi/qapi-builtin-visit.h"
>   #include "qemu/units.h"
>   #if defined(CONFIG_USER_ONLY)
> @@ -47,7 +48,7 @@
>   struct TCGState {
>       AccelState parent_obj;
>   
> -    bool mttcg_enabled;
> +    OnOffAuto mttcg_enabled;
>       bool one_insn_per_tb;
>       int splitwx_enabled;
>       unsigned long tb_size;
> @@ -68,37 +69,10 @@ bool qemu_tcg_mttcg_enabled(void)
>   }
>   #endif
>   
> -/*
> - * We default to false if we know other options have been enabled
> - * which are currently incompatible with MTTCG. Otherwise when each
> - * guest (target) has been updated to support:
> - *   - atomic instructions
> - *   - memory ordering primitives (barriers)
> - * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
> - *
> - * Once a guest architecture has been converted to the new primitives
> - * there is one remaining limitation to check:
> - *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
> - */
> -
> -static bool default_mttcg_enabled(void)
> -{
> -    if (icount_enabled()) {
> -        return false;
> -    }
> -#ifdef TARGET_SUPPORTS_MTTCG
> -    return true;
> -#else
> -    return false;
> -#endif
> -}
> -
>   static void tcg_accel_instance_init(Object *obj)
>   {
>       TCGState *s = TCG_STATE(obj);
>   
> -    s->mttcg_enabled = default_mttcg_enabled();
> -
>       /* If debugging enabled, default "auto on", otherwise off. */
>   #if defined(CONFIG_DEBUG_TCG) && !defined(CONFIG_USER_ONLY)
>       s->splitwx_enabled = -1;
> @@ -117,8 +91,37 @@ static int tcg_init_machine(MachineState *ms)
>   #else
>       unsigned max_cpus = ms->smp.max_cpus;
>   #endif
> +#ifdef TARGET_SUPPORTS_MTTCG
> +    bool mttcg_supported = true;
> +#else
> +    bool mttcg_supported = false;
> +#endif
>   
>       tcg_allowed = true;
> +
> +    if (s->mttcg_enabled == ON_OFF_AUTO_AUTO) {
> +        /*
> +         * We default to false if we know other options have been enabled
> +         * which are currently incompatible with MTTCG. Otherwise when each
> +         * guest (target) has been updated to support:
> +         *   - atomic instructions
> +         *   - memory ordering primitives (barriers)
> +         * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
> +         *
> +         * Once a guest architecture has been converted to the new primitives
> +         * there is one remaining limitation to check:
> +         *   - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
> +         */
> +        if (icount_enabled()) {
> +            s->mttcg_enabled = ON_OFF_AUTO_OFF;
> +        } else {
> +            s->mttcg_enabled = mttcg_supported;
> +        }
> +    }
> +    if (s->mttcg_enabled == ON_OFF_AUTO_ON && !mttcg_supported) {
> +        warn_report("Guest not yet converted to MTTCG - "
> +                    "you may get unexpected results");
> +    }
>       mttcg_enabled = s->mttcg_enabled;
>   
>       page_init();
> @@ -144,7 +147,7 @@ static char *tcg_get_thread(Object *obj, Error **errp)
>   {
>       TCGState *s = TCG_STATE(obj);
>   
> -    return g_strdup(s->mttcg_enabled ? "multi" : "single");
> +    return g_strdup(s->mttcg_enabled == ON_OFF_AUTO_ON ? "multi" : "single");
>   }
>   
>   static void tcg_set_thread(Object *obj, const char *value, Error **errp)
> @@ -155,14 +158,10 @@ static void tcg_set_thread(Object *obj, const char *value, Error **errp)
>           if (icount_enabled()) {
>               error_setg(errp, "No MTTCG when icount is enabled");
>           } else {
> -#ifndef TARGET_SUPPORTS_MTTCG
> -            warn_report("Guest not yet converted to MTTCG - "
> -                        "you may get unexpected results");
> -#endif
> -            s->mttcg_enabled = true;
> +            s->mttcg_enabled = ON_OFF_AUTO_ON;
>           }
>       } else if (strcmp(value, "single") == 0) {
> -        s->mttcg_enabled = false;
> +        s->mttcg_enabled = ON_OFF_AUTO_OFF;
>       } else {
>           error_setg(errp, "Invalid 'thread' setting %s", value);
>       }

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>