clk: imx: lpcg: add suspend/resume support

LPCG clock state may be lost when it's power domain is completely
off during system suspend/resume and we need save and restore the
state properly.
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/clk/imx/clk-imx8qxp-lpcg.c

@@ -364,6 +364,7 @@ static struct platform_driver imx8qxp_lpcg_clk_driver = {
 	.driver = {
 		.name = "imx8qxp-lpcg-clk",
 		.of_match_table = imx8qxp_lpcg_match,
+		.pm = &imx_clk_lpcg_scu_pm_ops,
 		.suppress_bind_attrs = true,
 	},
 	.probe = imx8qxp_lpcg_clk_probe,

drivers/clk/imx/clk-lpcg-scu.c

@@ -34,6 +34,9 @@ struct clk_lpcg_scu {
 	void __iomem *reg;
 	u8 bit_idx;
 	bool hw_gate;
+
+	/* for state save&restore */
+	u32 state;
 };
 
 #define to_clk_lpcg_scu(_hw) container_of(_hw, struct clk_lpcg_scu, hw)
@@ -113,6 +116,9 @@ struct clk_hw *__imx_clk_lpcg_scu(struct device *dev, const char *name,
 		hw = ERR_PTR(ret);
 	}
 
+	if (dev)
+		dev_set_drvdata(dev, clk);
+
 	return hw;
 }
 
@@ -123,3 +129,34 @@ void imx_clk_lpcg_scu_unregister(struct clk_hw *hw)
 	clk_hw_unregister(&clk->hw);
 	kfree(clk);
 }
+
+static int __maybe_unused imx_clk_lpcg_scu_suspend(struct device *dev)
+{
+	struct clk_lpcg_scu *clk = dev_get_drvdata(dev);
+
+	clk->state = readl_relaxed(clk->reg);
+	dev_dbg(dev, "save lpcg state 0x%x\n", clk->state);
+
+	return 0;
+}
+
+static int __maybe_unused imx_clk_lpcg_scu_resume(struct device *dev)
+{
+	struct clk_lpcg_scu *clk = dev_get_drvdata(dev);
+
+	/*
+	 * FIXME: Sometimes writes don't work unless the CPU issues
+	 * them twice
+	 */
+
+	writel(clk->state, clk->reg);
+	writel(clk->state, clk->reg);
+	dev_dbg(dev, "restore lpcg state 0x%x\n", clk->state);
+
+	return 0;
+}
+
+const struct dev_pm_ops imx_clk_lpcg_scu_pm_ops = {
+	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(imx_clk_lpcg_scu_suspend,
+				      imx_clk_lpcg_scu_resume)
+};

drivers/clk/imx/clk-scu.h

@@ -11,6 +11,7 @@
 #include <linux/of.h>
 
 extern struct list_head imx_scu_clks[];
+extern const struct dev_pm_ops imx_clk_lpcg_scu_pm_ops;
 
 int imx_clk_scu_init(struct device_node *np);
 struct clk_hw *imx_scu_of_clk_src_get(struct of_phandle_args *clkspec,