drivers: qcom: rpmh-rsc: Check cmd_db_ready() to help children

Children of RPMh will need access to cmd_db.  Rather than having each
child have code to check if cmd_db is ready let's add the check to
RPMh.

With this we'll be able to remove this boilerplate code from
clk-rpmh.c and qcom-rpmh-regulator.c.  Neither of these files has
landed upstream yet but patches are pretty far along.

===
This code is based upon v11 of Lina and Raju's RPMh series.
Suggested-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>

drivers/soc/qcom/rpmh-rsc.c

@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 
+#include <soc/qcom/cmd-db.h>
 #include <soc/qcom/tcs.h>
 #include <dt-bindings/soc/qcom,rpmh-rsc.h>
 
@@ -621,6 +622,18 @@ static int rpmh_rsc_probe(struct platform_device *pdev)
 	struct rsc_drv *drv;
 	int ret, irq;
 
+	/*
+	 * Even though RPMh doesn't directly use cmd-db, all of its children
+	 * do. To avoid adding this check to our children we'll do it now.
+	 */
+	ret = cmd_db_ready();
+	if (ret) {
+		if (ret != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "Command DB not available (%d)\n",
+									ret);
+		return ret;
+	}
+
 	drv = devm_kzalloc(&pdev->dev, sizeof(*drv), GFP_KERNEL);
 	if (!drv)
 		return -ENOMEM;