rpmsg: qcom_smd: Use qcom_smem_is_available()

Rather than looking up a dummy item from SMEM, use the new
qcom_smem_is_available() function to make the code more clear
(and reduce the overhead slightly).

Add the same check to qcom_smd_register_edge() as well to ensure that
it only succeeds if SMEM is already available - if a driver calls the
function and SMEM is not available yet then the initial state will be
read incorrectly and the RPMSG devices might never become available.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20230531-rpm-rproc-v3-8-a07dcdefd918@gerhold.net
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

Author: stephan-gh

drivers/rpmsg/qcom_smd.c

@@ -1479,6 +1479,9 @@ struct qcom_smd_edge *qcom_smd_register_edge(struct device *parent,
 	struct qcom_smd_edge *edge;
 	int ret;
 
+	if (!qcom_smem_is_available())
+		return ERR_PTR(-EPROBE_DEFER);
+
 	edge = kzalloc(sizeof(*edge), GFP_KERNEL);
 	if (!edge)
 		return ERR_PTR(-ENOMEM);
@@ -1553,12 +1556,9 @@ EXPORT_SYMBOL(qcom_smd_unregister_edge);
 static int qcom_smd_probe(struct platform_device *pdev)
 {
 	struct device_node *node;
-	void *p;
 
-	/* Wait for smem */
-	p = qcom_smem_get(QCOM_SMEM_HOST_ANY, smem_items[0].alloc_tbl_id, NULL);
-	if (PTR_ERR(p) == -EPROBE_DEFER)
-		return PTR_ERR(p);
+	if (!qcom_smem_is_available())
+		return -EPROBE_DEFER;
 
 	for_each_available_child_of_node(pdev->dev.of_node, node)
 		qcom_smd_register_edge(&pdev->dev, node);