drm/msm/a6xx: add module param to enable debugbus snapshot

For production devices, the debugbus sections will typically be fused
off and empty in the gpu device coredump.  But since this may contain
data like cache contents, don't capture it by default.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a6xx_gpu_state.c

@@ -938,7 +938,8 @@ struct msm_gpu_state *a6xx_gpu_state_get(struct msm_gpu *gpu)
 		msm_gem_kernel_put(dumper.bo, gpu->aspace, true);
 	}
 
-	a6xx_get_debugbus(gpu, a6xx_state);
+	if (snapshot_debugbus)
+		a6xx_get_debugbus(gpu, a6xx_state);
 
 	return  &a6xx_state->base;
 }

drivers/gpu/drm/msm/adreno/adreno_device.c

@@ -14,6 +14,10 @@ bool hang_debug = false;
 MODULE_PARM_DESC(hang_debug, "Dump registers when hang is detected (can be slow!)");
 module_param_named(hang_debug, hang_debug, bool, 0600);
 
+bool snapshot_debugbus = false;
+MODULE_PARM_DESC(snapshot_debugbus, "Include debugbus sections in GPU devcoredump (if not fused off)");
+module_param_named(snapshot_debugbus, snapshot_debugbus, bool, 0600);
+
 static const struct adreno_info gpulist[] = {
 	{
 		.rev   = ADRENO_REV(2, 0, 0, 0),

drivers/gpu/drm/msm/adreno/adreno_gpu.h

@@ -21,6 +21,8 @@
 #define REG_SKIP ~0
 #define REG_ADRENO_SKIP(_offset) [_offset] = REG_SKIP
 
+extern bool snapshot_debugbus;
+
 /**
  * adreno_regs: List of registers that are used in across all
  * 3D devices. Each device type has different offset value for the same