ASoC: imx-audmux: Add driver suspend and resume to support MEGA Fast

For i.MX6 SoloX, there is a mode of the SoC to shutdown all power
source of modules during system suspend and resume procedure.
Thus, AUDMUX needs to save all the values of registers before the
system suspend and restore them after the system resume.
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1565931794-7218-1-git-send-email-shengjiu.wang@nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/imx-audmux.c

@@ -23,6 +23,8 @@
 
 static struct clk *audmux_clk;
 static void __iomem *audmux_base;
+static u32 *regcache;
+static u32 reg_max;
 
 #define IMX_AUDMUX_V2_PTCR(x)		((x) * 8)
 #define IMX_AUDMUX_V2_PDCR(x)		((x) * 8 + 4)
@@ -317,8 +319,23 @@ static int imx_audmux_probe(struct platform_device *pdev)
 	if (of_id)
 		pdev->id_entry = of_id->data;
 	audmux_type = pdev->id_entry->driver_data;
-	if (audmux_type == IMX31_AUDMUX)
+
+	switch (audmux_type) {
+	case IMX31_AUDMUX:
 		audmux_debugfs_init();
+		reg_max = 14;
+		break;
+	case IMX21_AUDMUX:
+		reg_max = 6;
+		break;
+	default:
+		dev_err(&pdev->dev, "unsupported version!\n");
+		return -EINVAL;
+	}
+
+	regcache = devm_kzalloc(&pdev->dev, sizeof(u32) * reg_max, GFP_KERNEL);
+	if (!regcache)
+		return -ENOMEM;
 
 	if (of_id)
 		imx_audmux_parse_dt_defaults(pdev, pdev->dev.of_node);
@@ -334,12 +351,47 @@ static int imx_audmux_remove(struct platform_device *pdev)
 	return 0;
 }
 
+#ifdef CONFIG_PM_SLEEP
+static int imx_audmux_suspend(struct device *dev)
+{
+	int i;
+
+	clk_prepare_enable(audmux_clk);
+
+	for (i = 0; i < reg_max; i++)
+		regcache[i] = readl(audmux_base + i * 4);
+
+	clk_disable_unprepare(audmux_clk);
+
+	return 0;
+}
+
+static int imx_audmux_resume(struct device *dev)
+{
+	int i;
+
+	clk_prepare_enable(audmux_clk);
+
+	for (i = 0; i < reg_max; i++)
+		writel(regcache[i], audmux_base + i * 4);
+
+	clk_disable_unprepare(audmux_clk);
+
+	return 0;
+}
+#endif /* CONFIG_PM_SLEEP */
+
+static const struct dev_pm_ops imx_audmux_pm = {
+	SET_SYSTEM_SLEEP_PM_OPS(imx_audmux_suspend, imx_audmux_resume)
+};
+
 static struct platform_driver imx_audmux_driver = {
 	.probe		= imx_audmux_probe,
 	.remove		= imx_audmux_remove,
 	.id_table	= imx_audmux_ids,
 	.driver	= {
 		.name	= DRIVER_NAME,
+		.pm = &imx_audmux_pm,
 		.of_match_table = imx_audmux_dt_ids,
 	}
 };