intel/decoders: limit number of decoded batchbuffers

IGT has a test to hang the GPU that works by having a batch buffer
jump back into itself, trigger an infinite loop on the command stream.
As our implementation of the decoding is "perfectly" mimicking the
hardware, our decoder also "hangs". This change limits the number of
batch buffer we'll decode before we bail to 100.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>

src/intel/common/gen_batch_decoder.c

@@ -810,6 +810,17 @@ gen_print_batch(struct gen_batch_decode_ctx *ctx,
    const uint32_t *p, *end = batch + batch_size / sizeof(uint32_t);
    int length;
    struct gen_group *inst;
+   const char *reset_color = ctx->flags & GEN_BATCH_DECODE_IN_COLOR ? NORMAL : "";
+
+   if (ctx->n_batch_buffer_start >= 100) {
+      fprintf(ctx->fp, "%s0x%08"PRIx64": Max batch buffer jumps exceeded%s\n",
+              (ctx->flags & GEN_BATCH_DECODE_IN_COLOR) ? RED_COLOR : "",
+              (ctx->flags & GEN_BATCH_DECODE_OFFSETS) ? batch_addr : 0,
+              reset_color);
+      return;
+   }
+
+   ctx->n_batch_buffer_start++;
 
    for (p = batch; p < end; p += length) {
       inst = gen_ctx_find_instruction(ctx, p);
@@ -817,8 +828,6 @@ gen_print_batch(struct gen_batch_decode_ctx *ctx,
       assert(inst == NULL || length > 0);
       length = MAX2(1, length);
 
-      const char *reset_color = ctx->flags & GEN_BATCH_DECODE_IN_COLOR ? NORMAL : "";
-
       uint64_t offset;
       if (ctx->flags & GEN_BATCH_DECODE_OFFSETS)
          offset = batch_addr + ((char *)p - (char *)batch);
@@ -908,4 +917,6 @@ gen_print_batch(struct gen_batch_decode_ctx *ctx,
          break;
       }
    }
+
+   ctx->n_batch_buffer_start--;
 }

src/intel/common/gen_decoder.h

@@ -237,6 +237,8 @@ struct gen_batch_decode_ctx {
    int max_vbo_decoded_lines;
 
    enum drm_i915_gem_engine_class engine;
+
+   int n_batch_buffer_start;
 };
 
 void gen_batch_decode_ctx_init(struct gen_batch_decode_ctx *ctx,