clk: mediatek: clk-mtk: Add dummy clock ops

In order to migrate some (few) old clock drivers to the common
mtk_clk_simple_probe() function, add dummy clock ops to be able
to insert a dummy clock with ID 0 at the beginning of the list.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Miles Chen <miles.chen@mediatek.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Miles Chen <miles.chen@mediatek.com>
Link: https://lore.kernel.org/r/20230120092053.182923-8-angelogioacchino.delregno@collabora.com
Tested-by: Mingming Su <mingming.su@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/mediatek/clk-mtk.c

@@ -18,6 +18,22 @@
 #include "clk-mtk.h"
 #include "clk-gate.h"
 
+const struct mtk_gate_regs cg_regs_dummy = { 0, 0, 0 };
+EXPORT_SYMBOL_GPL(cg_regs_dummy);
+
+static int mtk_clk_dummy_enable(struct clk_hw *hw)
+{
+	return 0;
+}
+
+static void mtk_clk_dummy_disable(struct clk_hw *hw) { }
+
+const struct clk_ops mtk_clk_dummy_ops = {
+	.enable		= mtk_clk_dummy_enable,
+	.disable	= mtk_clk_dummy_disable,
+};
+EXPORT_SYMBOL_GPL(mtk_clk_dummy_ops);
+
 static void mtk_init_clk_data(struct clk_hw_onecell_data *clk_data,
 			      unsigned int clk_num)
 {

drivers/clk/mediatek/clk-mtk.h

@@ -22,6 +22,25 @@
 
 struct platform_device;
 
+/*
+ * We need the clock IDs to start from zero but to maintain devicetree
+ * backwards compatibility we can't change bindings to start from zero.
+ * Only a few platforms are affected, so we solve issues given by the
+ * commonized MTK clocks probe function(s) by adding a dummy clock at
+ * the beginning where needed.
+ */
+#define CLK_DUMMY		0
+
+extern const struct clk_ops mtk_clk_dummy_ops;
+extern const struct mtk_gate_regs cg_regs_dummy;
+
+#define GATE_DUMMY(_id, _name) {				\
+		.id = _id,					\
+		.name = _name,					\
+		.regs = &cg_regs_dummy,				\
+		.ops = &mtk_clk_dummy_ops,			\
+	}
+
 struct mtk_fixed_clk {
 	int id;
 	const char *name;