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serial: ns16550: Support clocks via phandle

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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>
This commit is contained in:
Paul Burton 2016-09-08 07:47:29 +01:00 committed by Daniel Schwierzeck
parent 3f96f87520
commit 50fce1d5d8
1 changed files with 18 additions and 3 deletions
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21
drivers/serial/ns16550.c
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@ -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;