clk: mediatek: add CLK_BYPASS_XTAL flag to allow bypassing searching clock parent of xtal clock

The mtk clock framework in u-boot uses array index for searching clock
parent (kernel uses strings for search), so we need to specify a special
clock with ID=0 for CLK_XTAL in u-boot.

In the mt7622/mt7629 clock tree, the clocks with ID=0 never call
mtk_topckgen_get_mux_rate, adn return xtal clock directly. This what we
expected.

However for newer chips, they may have some clocks with ID=0 not
representing the xtal clock and still needs mtk_topckgen_get_mux_rate be
called. Current logic will make entire clock driver not working.

This patch adds a flag to indicate that whether a clock driver needs clocks
with ID=0 to call mtk_topckgen_get_mux_rate.

Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>

drivers/clk/mediatek/clk-mtk.c

@@ -319,7 +319,9 @@ static ulong mtk_topckgen_get_mux_rate(struct clk *clk, u32 off)
 	index &= mux->mux_mask << mux->mux_shift;
 	index = index >> mux->mux_shift;
 
-	if (mux->parent[index])
+	if (mux->parent[index] > 0 ||
+	    (mux->parent[index] == CLK_XTAL &&
+	     priv->tree->flags & CLK_BYPASS_XTAL))
 		return mtk_clk_find_parent_rate(clk, mux->parent[index],
 						NULL);
 

drivers/clk/mediatek/clk-mtk.h

@@ -11,6 +11,11 @@
 #define CLK_XTAL			0
 #define MHZ				(1000 * 1000)
 
+/* flags in struct mtk_clk_tree */
+
+/* clk id == 0 doesn't mean it's xtal clk */
+#define CLK_BYPASS_XTAL			BIT(0)
+
 #define HAVE_RST_BAR			BIT(0)
 #define CLK_DOMAIN_SCPSYS		BIT(0)
 #define CLK_MUX_SETCLR_UPD		BIT(1)
@@ -197,6 +202,7 @@ struct mtk_clk_tree {
 	const struct mtk_fixed_clk *fclks;
 	const struct mtk_fixed_factor *fdivs;
 	const struct mtk_composite *muxes;
+	u32 flags;
 };
 
 struct mtk_clk_priv {