mailbox: imx: Add context save/restore for suspend/resume

For "mem" mode suspend on i.MX8 SoCs, MU settings could be
lost because its power is off, so save/restore is needed
for MU settings during suspend/resume. However, the restore
can ONLY be done when MU settings are actually lost, for the
scenario of settings NOT lost in "freeze" mode suspend, since
there could be still IPC going on multiple CPUs, restoring the
MU settings could overwrite the TIE by mistake and cause system
freeze, so need to make sure ONLY restore the MU settings when
it is powered off, Anson fixes this by checking whether restore
is actually needed when resume.

Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/imx-mailbox.c

@@ -67,6 +67,8 @@ struct imx_mu_priv {
 	struct clk		*clk;
 	int			irq;
 
+	u32 xcr;
+
 	bool			side_b;
 };
 
@@ -589,12 +591,45 @@ static const struct of_device_id imx_mu_dt_ids[] = {
 };
 MODULE_DEVICE_TABLE(of, imx_mu_dt_ids);
 
+static int imx_mu_suspend_noirq(struct device *dev)
+{
+	struct imx_mu_priv *priv = dev_get_drvdata(dev);
+
+	priv->xcr = imx_mu_read(priv, priv->dcfg->xCR);
+
+	return 0;
+}
+
+static int imx_mu_resume_noirq(struct device *dev)
+{
+	struct imx_mu_priv *priv = dev_get_drvdata(dev);
+
+	/*
+	 * ONLY restore MU when context lost, the TIE could
+	 * be set during noirq resume as there is MU data
+	 * communication going on, and restore the saved
+	 * value will overwrite the TIE and cause MU data
+	 * send failed, may lead to system freeze. This issue
+	 * is observed by testing freeze mode suspend.
+	 */
+	if (!imx_mu_read(priv, priv->dcfg->xCR))
+		imx_mu_write(priv, priv->xcr, priv->dcfg->xCR);
+
+	return 0;
+}
+
+static const struct dev_pm_ops imx_mu_pm_ops = {
+	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(imx_mu_suspend_noirq,
+				      imx_mu_resume_noirq)
+};
+
 static struct platform_driver imx_mu_driver = {
 	.probe		= imx_mu_probe,
 	.remove		= imx_mu_remove,
 	.driver = {
 		.name	= "imx_mu",
 		.of_match_table = imx_mu_dt_ids,
+		.pm = &imx_mu_pm_ops,
 	},
 };
 module_platform_driver(imx_mu_driver);