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.bur...@imgtec.com>
Reviewed-by: Simon Glass <s...@chromium.org>
---
Changes in v6:
- Ignore -ENOSYS from clk_get_by_index too, for systems with CONFIG_CLK=n
Changes in v5: None
Changes in v4: None
Changes in v3: None
Changes in v2:
- Propogate non-ENODEV errors from clk_get_by_index
drivers/serial/ns16550.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 88fca15..af317cb 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 +400,19 @@ 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);
+ } 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;
--
2.9.2
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