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 ---
drivers/serial/ns16550.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c index 88fca15..53032dc 100644 --- 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 +400,14 @@ 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) + plat->clock = clk_get_rate(&clk); + 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;