serial: ns16550: Support clocks via phandle

Previously ns16550 compatible UARTs probed via device tree have needed
their device tree nodes to contain a clock-frequency property. An
alternative to this commonly used with Linux is to reference a clock via
a phandle. This patch allows U-Boot to support that, retrieving the
clock frequency by probing the appropriate clock device.

For example, a system might choose to provide the UART base clock as a
reference to a clock common to multiple devices:

  sys_clk: clock {
    compatible = "fixed-clock";
    #clock-cells = <0>;
    clock-frequency = <10000000>;
  };

  uart0: uart@10000000 {
    compatible = "ns16550a";
    reg = <0x10000000 0x1000>;
    clocks = <&sys_clk>;
  };

  uart1: uart@10000000 {
    compatible = "ns16550a";
    reg = <0x10001000 0x1000>;
    clocks = <&sys_clk>;
  };

This removes the need for the frequency information to be duplicated in
multiple nodes and allows the device tree to be more descriptive of the
system.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 88fca15357e6414915427d79d561669d67a156d9..3f6ea4d27591233836977c84450c5d7aac96f824 100644 (file)
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <clk.h>
 #include <dm.h>
 #include <errno.h>
 #include <fdtdec.h>
@@ -352,6 +353,8 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
 {
        struct ns16550_platdata *plat = dev->platdata;
        fdt_addr_t addr;
+       struct clk clk;
+       int err;
 
        /* try Processor Local Bus device first */
        addr = dev_get_addr(dev);
@@ -397,9 +400,21 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
                                     "reg-offset", 0);
        plat->reg_shift = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
                                         "reg-shift", 0);
-       plat->clock = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
-                                    "clock-frequency",
-                                    CONFIG_SYS_NS16550_CLK);
+
+       err = clk_get_by_index(dev, 0, &clk);
+       if (!err) {
+               err = clk_get_rate(&clk);
+               if (!IS_ERR_VALUE(err))
+                       plat->clock = err;
+       } else if (err != -ENODEV && err != -ENOSYS) {
+               debug("ns16550 failed to get clock\n");
+               return err;
+       }
+
+       if (!plat->clock)
+               plat->clock = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
+                                            "clock-frequency",
+                                            CONFIG_SYS_NS16550_CLK);
        if (!plat->clock) {
                debug("ns16550 clock not defined\n");
                return -EINVAL;