drm/selftests/test-drm_dp_mst_helper: Place 'struct drm_dp_sideband_msg_req_body' onto the heap

The stack is too full.

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c: In function ‘sideband_msg_req_encode_decode’:
 drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c:161:1: warning: the frame size of 1176 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Lyude Paul <lyude@redhat.com>
Cc: David Francis <David.Francis@amd.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201116174112.1833368-30-lee.jones@linaro.org

drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c

@@ -120,44 +120,53 @@ sideband_msg_req_equal(const struct drm_dp_sideband_msg_req_body *in,
 static bool
 sideband_msg_req_encode_decode(struct drm_dp_sideband_msg_req_body *in)
 {
-	struct drm_dp_sideband_msg_req_body out = {0};
+	struct drm_dp_sideband_msg_req_body *out;
 	struct drm_printer p = drm_err_printer(PREFIX_STR);
 	struct drm_dp_sideband_msg_tx txmsg;
 	int i, ret;
+	bool result = true;
+
+	out = kzalloc(sizeof(*out), GFP_KERNEL);
+	if (!out)
+		return false;
 
 	drm_dp_encode_sideband_req(in, &txmsg);
-	ret = drm_dp_decode_sideband_req(&txmsg, &out);
+	ret = drm_dp_decode_sideband_req(&txmsg, out);
 	if (ret < 0) {
 		drm_printf(&p, "Failed to decode sideband request: %d\n",
 			   ret);
-		return false;
+		result = false;
+		goto out;
 	}
 
-	if (!sideband_msg_req_equal(in, &out)) {
+	if (!sideband_msg_req_equal(in, out)) {
 		drm_printf(&p, "Encode/decode failed, expected:\n");
 		drm_dp_dump_sideband_msg_req_body(in, 1, &p);
 		drm_printf(&p, "Got:\n");
-		drm_dp_dump_sideband_msg_req_body(&out, 1, &p);
-		return false;
+		drm_dp_dump_sideband_msg_req_body(out, 1, &p);
+		result = false;
+		goto out;
 	}
 
 	switch (in->req_type) {
 	case DP_REMOTE_DPCD_WRITE:
-		kfree(out.u.dpcd_write.bytes);
+		kfree(out->u.dpcd_write.bytes);
 		break;
 	case DP_REMOTE_I2C_READ:
-		for (i = 0; i < out.u.i2c_read.num_transactions; i++)
-			kfree(out.u.i2c_read.transactions[i].bytes);
+		for (i = 0; i < out->u.i2c_read.num_transactions; i++)
+			kfree(out->u.i2c_read.transactions[i].bytes);
 		break;
 	case DP_REMOTE_I2C_WRITE:
-		kfree(out.u.i2c_write.bytes);
+		kfree(out->u.i2c_write.bytes);
 		break;
 	}
 
 	/* Clear everything but the req_type for the input */
 	memset(&in->u, 0, sizeof(in->u));
 
-	return true;
+out:
+	kfree(out);
+	return result;
 }
 
 int igt_dp_mst_sideband_msg_req_decode(void *unused)