In function wm831x_fll_is_prepared() defined in file drivers/clk/clk-wm831x.c, it returns true (at line 82) when the call to wm831x_reg_read() (at line 78) fails. I am not sure whether it is a bug. From the name of the function, I guess "true" indicates that the wm831x_clkout is already prepared. So, when wm831x_reg_read() fails, returns "true" seems improper. Related codes are shown as follows.

wm831x_fll_is_prepared @@ drivers/clk/clk-wm831x.c
 71 static int wm831x_fll_is_prepared(struct clk_hw *hw)
 72 {
 73     struct wm831x_clk *clkdata = container_of(hw, struct wm831x_clk,
 74                           fll_hw);
 75     struct wm831x *wm831x = clkdata->wm831x;
 76     int ret;
 77 
 78     ret = wm831x_reg_read(wm831x, WM831X_FLL_CONTROL_1);
 79     if (ret < 0) {
 80         dev_err(wm831x->dev, "Unable to read FLL_CONTROL_1: %d\n",
 81             ret);
 82         return true; // Bug: seems improper
 83     }
 84 
 85     return (ret & WM831X_FLL_ENA) != 0;
 86 }

Thanks very much!