UART_INIT_CLOCK not modifying baud_base

[Lelek]

Dear all,
I just realized there is a bug in (probably) kernel and its pl011 driver, regarding bcm2709:
Putting in /boot/config.txt line:

init_uart_clock=14746000

alters the PLL and UART clocks, which can be checked with:

root@xxxxx:~# vcgencmd measure_clock uart
frequency(22)=14746000

But baud_base is not up to par with the clock, it's still reported as 187500:

root@xxxxx:~# setserial -G /dev/ttyAMA0
/dev/ttyAMA0 uart undefined port 0x0000 irq 83 baud_base 187500 spd_normal

Thereby any baud rate being set is invalid. The only workaround to make UART work with 921600 was to set init_uart_clock to 24M and set baud rate of UART to 115200. But it's only a dirty workaround.

[Lelek (lelek-spam)]

Tested on Raspberry Pi 2, with stock 3.18 and freshly built 4.0.7 kernels.

[peter green (plugwash)]

Please report this to the raspberry pi foundation and report back when they have a fix.