[RFC v8 40/44] accel: add double dispatch mechanism for class initialization

[Claudio Fontana]

while on x86 all CPU classes can use the same set of TCGCPUOps,
on ARM the right accel behavior depends on the type of the CPU.

So we need a way to specialize the accel behavior according to
the CPU. Therefore, add a second initialization, after the
accel_cpu->cpu_class_init, that allows to do this.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
---
 include/hw/core/cpu.h     |  6 ++++++
 accel/accel-common.c      | 12 ++++++++++++
 target/i386/tcg/tcg-cpu.c |  8 +++++++-
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index c68bc3ba8a..d45f78290e 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -192,6 +192,12 @@ struct CPUClass {
 
     /* when TCG is not available, this pointer is NULL */
     struct TCGCPUOps *tcg_ops;
+
+    /*
+     * if not NULL, this is called in order for the CPUClass to initialize
+     * class data that depends on the accelerator, see accel/accel-common.c.
+     */
+    void (*init_accel_cpu)(struct AccelCPUClass *accel_cpu, CPUClass *cc);
 };
 
 /*
diff --git a/accel/accel-common.c b/accel/accel-common.c
index d77c09d7b5..2103397d5e 100644
--- a/accel/accel-common.c
+++ b/accel/accel-common.c
@@ -54,10 +54,22 @@ static void accel_init_cpu_int_aux(ObjectClass *klass, void 
*opaque)
     CPUClass *cc = CPU_CLASS(klass);
     AccelCPUClass *accel_cpu = opaque;
 
+    /*
+     * double dispatch. The first callback allows the accel cpu
+     * to run initializations for the CPU,
+     * the second one allows the CPU to customize the accel cpu
+     * behavior according to the CPU.
+     *
+     * The second is currently only used by TCG, to specialize the
+     * TCGCPUOps depending on the CPU type.
+     */
     cc->accel_cpu = accel_cpu;
     if (accel_cpu->cpu_class_init) {
         accel_cpu->cpu_class_init(cc);
     }
+    if (cc->init_accel_cpu) {
+        cc->init_accel_cpu(accel_cpu, cc);
+    }
 }
 
 /* initialize the arch-specific accel CpuClass interfaces */
diff --git a/target/i386/tcg/tcg-cpu.c b/target/i386/tcg/tcg-cpu.c
index e311f52855..ba39531aa5 100644
--- a/target/i386/tcg/tcg-cpu.c
+++ b/target/i386/tcg/tcg-cpu.c
@@ -69,11 +69,17 @@ static struct TCGCPUOps x86_tcg_ops = {
 #endif /* !CONFIG_USER_ONLY */
 };
 
-static void tcg_cpu_class_init(CPUClass *cc)
+static void tcg_cpu_init_ops(AccelCPUClass *accel_cpu, CPUClass *cc)
 {
+    /* for x86, all cpus use the same set of operations */
     cc->tcg_ops = &x86_tcg_ops;
 }
 
+static void tcg_cpu_class_init(CPUClass *cc)
+{
+    cc->init_accel_cpu = tcg_cpu_init_ops;
+}
+
 /*
  * TCG-specific defaults that override all CPU models when using TCG
  */
-- 
2.26.2