I am working on an embedded Project with Minnowboard Max and customized Linux kernel with u-boot.
The Kernel command line parameters:
initcall_debug=1 video=HDMI-A-1:1920x1200MR@60D console=ttyS0,115200 console=tty0
debug_putstr("\nDecompressing Linux... ");
Is there any way to see these messages in the serial port?
Salient information is the processor architecture.
For instance in ARM booting, the decompressor code uses its own serial port configuration which is distinct from earlyprintk. Some ARM machines have config dialog to specify this early serial port; some might use the machine ID (see How do I find ARM Linux entry point when it fails to uncompress?). On ARM earlyprintk is not effective untill after the (init/main.c) init_kernel() routine has started.
For x86 all early serial port configuration & I/O is consolidated into the earlyprintk feature. Use the kernel command line parameter to define the serial port (default is device at 0x3F8) and baud rate (default is 9600).
1081 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] 1082 earlyprintk=vga 1083 earlyprintk=efi 1084 earlyprintk=xen 1085 earlyprintk=serial[,ttySn[,baudrate]] 1086 earlyprintk=serial[,0x...[,baudrate]] 1087 earlyprintk=ttySn[,baudrate] 1088 earlyprintk=dbgp[debugController#] 1089 earlyprintk=pciserial,bus:device.function[,baudrate] 1090 1091 earlyprintk is useful when the kernel crashes before 1092 the normal console is initialized. It is not enabled by 1093 default because it has some cosmetic problems. 1094 1095 Append ",keep" to not disable it when the real console 1096 takes over. 1097 1098 Only one of vga, efi, serial, or usb debug port can 1099 be used at a time. 1100 1101 Currently only ttyS0 and ttyS1 may be specified by 1102 name. Other I/O ports may be explicitly specified 1103 on some architectures (x86 and arm at least) by 1104 replacing ttySn with an I/O port address, like this: 1105 earlyprintk=serial,0x1008,115200 1106 You can find the port for a given device in 1107 /proc/tty/driver/serial: 1108 2: uart:ST16650V2 port:00001008 irq:18 ... 1109 1110 Interaction with the standard serial driver is not 1111 very good. 1112 1113 The VGA and EFI output is eventually overwritten by 1114 the real console. 1115 1116 The xen output can only be used by Xen PV guests.