how to get a clock from a device tree node - c

Question

I have the following issue: I want to define the clock a CPU should use during frequency transitions in the device tree rather than in the clock driver code (in this way it will be more generic). I want to define the "transition-clock" property in the device tree, something like:
232 cpu: cpu#01c20050 {
233 #clock-cells = <0>;
234 compatible = "allwinner,sun4i-a10-cpu-clk";
235 reg = <0x01c20050 0x4>;
-----
243 clocks = <&osc32k>, <&osc24M>, <&pll1>, <&pll1>;
244 transition-clock = <&osc24M>;
245 clock-output-names = "cpu";
246 };
I changed the file "drivers/clk/clkdev.c" to search this property so I can get a clk pointer and store it in a new property in the cpu clock structure. This is what I have managed so far (changes begin on line 78):
59 static struct clk *__of_clk_get(struct device_node *np, int index,
60 const char *dev_id, const char *con_id)
61 {
62 struct of_phandle_args clkspec;
63 struct clk *clk, *transition_clk;
64 struct device_node *clock_node, *transition_clock_node;
65 int rc;
66
67 if (index < 0)
68 return ERR_PTR(-EINVAL);
69
70 rc = of_parse_phandle_with_args(np, "clocks", "#clock-cells", index,
71 &clkspec);
72 if (rc)
73 return ERR_PTR(rc);
74
75 clk = __of_clk_get_by_clkspec(&clkspec, dev_id, con_id);
76 of_node_put(clkspec.np);
77
78 clock_node = of_parse_phandle(np, "clocks", 0);
79 pr_err("-------------------- parsing node %s\n", np->name);
80 if (clock_node!=NULL) {
81 pr_err("============ Clock node found %p\n", clock_node);
82 transition_clock_node =
83 of_parse_phandle(clock_node, "transition-clock", 0);
84 if (transition_clock_node!=NULL) {
85 pr_err("============ Transition clock node found %p\n",
86 transition_clock_node);
87 transition_clk = clk_get(clock_node, 0);
88 pr_err("============ Transition clock %p\n", transition_clk);
89 }
90 }
91
92 return clk;
93 }
I get pointers to the clock node and the transition clock node, but when I try to get a clock pointer from that, I get 0xfffffffe, which looks like an error:
[ 2.540542] -------------------- parsing node cpu
[ 2.540546] ============ Clock node found eeef9520
[ 2.540550] ============ Transition clock node found eeef8934
[ 2.540555] ============ Transition clock fffffffe
I want a clock object which I can later use in
clk_set_parent(cpu_clk, cpu_clk->transition_clk)
Any ideas are welcome :)

Answer 1

OK, I got it figured out in the meantime and since nobody answered I'm going to provide my solution (maybe somebody else bumps into this issue):
81 if (clock_node != NULL) {
82 rc = of_parse_phandle_with_args(clock_node, "transition-clock", NULL,
83 0, &transition_clkspec);
84 of_node_put(transition_clkspec.np);
85
86 if (!rc) {
87 transition_clock = __of_clk_get_by_clkspec(&transition_clkspec,
88 dev_id, con_id);
89 clk_set_transition_parent(clk, transition_clock);
90 }
91 }
So, the solution is to get an object of type "of_phandle_args" and get the clock from there using __of_clk_get_by_clkspec.
(the clk_set_transition_parent function is defined somewhere else and it does exactly what it's name suggests)