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From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC v3 PATCH 01/14] Introduce TCGOpcode for
 memory barrier
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To: Pranith Kumar <bobby.prani@gmail.com>, Richard Henderson <rth@twiddle.net>, "open list:All patches CC here" <qemu-devel@nongnu.org>
Cc: serge.fdrv@gmail.com, alex.bennee@linaro.org



On 18/06/2016 06:03, Pranith Kumar wrote:
> +typedef enum {
> +    TCG_MO_LD_LD    = 1,
> +    TCG_MO_ST_LD    = 2,
> +    TCG_MO_LD_ST    = 4,
> +    TCG_MO_ST_ST    = 8,

I like the idea of making this a bitmask.  However, most of the code you
wrote for the backends looks at these as an enum.  For example,


+static inline void tcg_out_mb(TCGContext *s, TCGArg a0)
+{
+    switch (a0 & TCG_MO_ALL) {
+    case TCG_MO_LD_LD:
+        tcg_out32(s, DMB_ISH | DMB_LD);
+        break;
+    case TCG_MO_ST_ST:
+        tcg_out32(s, DMB_ISH | DMB_ST);
+        break;
+    default:
+        tcg_out32(s, DMB_ISH | DMB_LD | DMB_ST);
+        break;
+    }
+}

should rather be

   if (a0 & (ST_LD|LD_ST)) {
       output dmb ish
       return
   }
   if (a0 & LD_LD) {
       output dmb ishld
   }
   if (a0 & LD_ST) {
       output dmb ishst
   }

Paolo

> +    TCG_MO_ALL      = 0xF, // OR of all above
> +} TCGOrder;
> +
> +typedef enum {
> +    TCG_BAR_ACQ     = 32,
> +    TCG_BAR_REL     = 64,
> +    TCG_BAR_SC      = 128,
> +} TCGBar;