Hi,
we are trying to solve one problem with early printk initialization
on Microblaze uart16550. I have also checked arm bootup code and
the situation is the same there (NOTE: This IP is possible to use on Zynq too).
The problem is about baudrate initialization. Current code just expect
that early console is initialized by previous bootloader/firmware (in our case
u-boot).
But if there is not initialization and directly elf is loaded there is no
initialization
done and kernel bootlog is shown when regular serial driver is probed.
I have create a solution which add baudrate initialization to Microblaze early
printk code.
And also two options how to load baudrate setting from device-tree.
Code expects that early console is specified in chosen node.
chosen {
linux,stdout-path = "/axi@0/serial@40400000";
} ;
Code finds out which IP it is and based on that initialize early printk driver.
Baudrate setting is counted from clock-frequency and current-speed defined
directly in uart node.
RS232_Uart_1: serial@40400000 {
clock-frequency = <50000000>;
compatible = "xlnx,axi-uart16550-1.01.a", "xlnx,xps-uart16550-2.00.a",
"ns16550a";
current-speed = <115200>;
device_type = "serial";
reg = < 0x40400000 0x10000 >;
reg-offset = <0x1000>;
reg-shift = <2>;
...irq, etc
} ;
This was the first version which is working but using current-speed is probably
not the best solution.
I have also create version where baudrate is directly specified in chosen node.
Clock frequency is still
loaded directly from the node.
chosen {
linux,stdout-path = "/axi@0/serial@40400000,115200";
} ;
What solution is more compatible with device-tree?
Thanks for you comments,
Michal
--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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