mailbox: imx: Support runtime PM

Some power hungry sub-systems like VPU has its own MUs which also
use mailbox driver, current mailbox driver uses platform driver
model and MU's power will be ON after driver probed and left ON
there, it may cause the whole sub-system can NOT enter lower power
mode, take VPU driver for example, it has runtime PM support, but
due to its MU always ON, the VPU sub-system will be always ON and
consume many power during kernel idle.

To save power in kernel idle, mailbox driver needs to support
runtime PM in order to power off MU when it is unused. However,
the runtime suspend/resume can ONLY be implemented in mailbox's
.shutdown/.startup callback, so its consumer needs to call
mbox_request_channel()/mbox_free_channel() in consumer driver's
runtime PM callback, then the MU's power will be ON/OFF along with
consumer's runtime PM status.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/imx-mailbox.c

@@ -12,6 +12,7 @@
 #include <linux/mailbox_controller.h>
 #include <linux/module.h>
 #include <linux/of_device.h>
+#include <linux/pm_runtime.h>
 #include <linux/slab.h>
 
 #define IMX_MU_xSR_GIPn(x)	BIT(28 + (3 - (x)))
@@ -287,6 +288,7 @@ static int imx_mu_startup(struct mbox_chan *chan)
 	struct imx_mu_con_priv *cp = chan->con_priv;
 	int ret;
 
+	pm_runtime_get_sync(priv->dev);
 	if (cp->type == IMX_MU_TYPE_TXDB) {
 		/* Tx doorbell don't have ACK support */
 		tasklet_init(&cp->txdb_tasklet, imx_mu_txdb_tasklet,
@@ -323,6 +325,7 @@ static void imx_mu_shutdown(struct mbox_chan *chan)
 
 	if (cp->type == IMX_MU_TYPE_TXDB) {
 		tasklet_kill(&cp->txdb_tasklet);
+		pm_runtime_put_sync(priv->dev);
 		return;
 	}
 
@@ -341,6 +344,7 @@ static void imx_mu_shutdown(struct mbox_chan *chan)
 	}
 
 	free_irq(priv->irq, chan);
+	pm_runtime_put_sync(priv->dev);
 }
 
 static const struct mbox_chan_ops imx_mu_ops = {
@@ -508,7 +512,27 @@ static int imx_mu_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, priv);
 
-	return devm_mbox_controller_register(dev, &priv->mbox);
+	ret = devm_mbox_controller_register(dev, &priv->mbox);
+	if (ret)
+		return ret;
+
+	pm_runtime_enable(dev);
+
+	ret = pm_runtime_get_sync(dev);
+	if (ret < 0) {
+		pm_runtime_put_noidle(dev);
+		goto disable_runtime_pm;
+	}
+
+	ret = pm_runtime_put_sync(dev);
+	if (ret < 0)
+		goto disable_runtime_pm;
+
+	return 0;
+
+disable_runtime_pm:
+	pm_runtime_disable(dev);
+	return ret;
 }
 
 static int imx_mu_remove(struct platform_device *pdev)
@@ -516,6 +540,7 @@ static int imx_mu_remove(struct platform_device *pdev)
 	struct imx_mu_priv *priv = platform_get_drvdata(pdev);
 
 	clk_disable_unprepare(priv->clk);
+	pm_runtime_disable(priv->dev);
 
 	return 0;
 }