[PATCH] serial: ns16550: Handle zero <clock-frequency> value

[Bin Meng]

A working device tree node of ns16550 should never be populated
with value zero for the <clock-frequency> property. Unfortunately
this is the case for the QEMU ppce500 target.

Let's try to assign plat->clock to CONFIG_SYS_NS16550_CLK as the
last resort to handle such case.

This commit should be reverted when:

- The following QEMU patch [1] is merged, and
- U-Boot CI has upgraded its QEMU version that contains the fix

[1] http://patchwork.ozlabs.org/project/qemu-devel/patch/1612362288-22216-2-git-send-email-bmeng.cn@gmail.com/

Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
---

 drivers/serial/ns16550.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index da903c1..a1593a2 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -563,6 +563,8 @@ int ns16550_serial_of_to_plat(struct udevice *dev)
 	if (!plat->clock)
 		plat->clock = dev_read_u32_default(dev, "clock-frequency",
 						   CONFIG_SYS_NS16550_CLK);
+	if (!plat->clock)
+		plat->clock = CONFIG_SYS_NS16550_CLK;
 	if (!plat->clock) {
 		debug("ns16550 clock not defined\n");
 		return -EINVAL;
-- 
2.7.4