clk: sprd: check its parent status before reading gate clock

Some clocks only can be accessed if their parent is enabled. mipi_csi_xx
clocks on SC9863A are an examples. We have to ensure the parent clock is
enabled when reading those clocks.
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lkml.kernel.org/r/20200527053638.31439-2-zhang.lyra@gmail.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/sprd/gate.c

@@ -94,8 +94,15 @@ static int sprd_gate_is_enabled(struct clk_hw *hw)
 {
 	struct sprd_gate *sg = hw_to_sprd_gate(hw);
 	struct sprd_clk_common *common = &sg->common;
+	struct clk_hw *parent;
 	unsigned int reg;
 
+	if (sg->flags & SPRD_GATE_NON_AON) {
+		parent = clk_hw_get_parent(hw);
+		if (!parent || !clk_hw_is_enabled(parent))
+			return 0;
+	}
+
 	regmap_read(common->regmap, common->reg, &reg);
 
 	if (sg->flags & CLK_GATE_SET_TO_DISABLE)

drivers/clk/sprd/gate.h

@@ -19,6 +19,15 @@ struct sprd_gate {
 	struct sprd_clk_common	common;
 };
 
+/*
+ * sprd_gate->flags is used for:
+ * CLK_GATE_SET_TO_DISABLE	BIT(0)
+ * CLK_GATE_HIWORD_MASK		BIT(1)
+ * CLK_GATE_BIG_ENDIAN		BIT(2)
+ * so we define new flags from	BIT(3)
+ */
+#define SPRD_GATE_NON_AON BIT(3) /* not alway powered on, check before read */
+
 #define SPRD_SC_GATE_CLK_HW_INIT_FN(_struct, _name, _parent, _reg,	\
 				    _sc_offset, _enable_mask, _flags,	\
 				    _gate_flags, _udelay, _ops, _fn)	\