+CC linux-serial On Thursday 14 May 2015 06:34 PM, Vineet Gupta wrote: > On Thursday 14 May 2015 06:23 PM, Arnd Bergmann wrote: > > On Thursday 14 May 2015 15:48:42 Alexey Brodkin wrote: > > >> > >> > chosen { >> > - bootargs = "console=tty0 console=ttyS3,115200n8 consoleblank=0"; >> > + bootargs = "earlycon=uart8250,mmio32,0xe0022000,115200n8 console=tty0 console=ttyS3,115200n8 consoleblank=0"; >> > }; >> > }; >> > > > When you do earlycon with DT, better use a 'stdout-path' property that points > to the device, and just put 'earlycon' without arguments on the command line. > > Arnd > > > Sure ! I tried that once (3.16) and even the dts patch got merged but had to be reverted out ! > > 2014-07-27 22524b02b17b Revert "ARC: [arcfpga] stdout-path now suffices for earlycon/console" > > Let me see if that works again since serial land has seen some significant churn in recent times > > Thx for pointing this out ! so specifying console with stdout-path works for me, - bootargs = "earlycon=uart8250,mmio32,0xf0000000,115200n8 console=tty0 console=ttyS0,115200n8 consoleblank=0 debug"; + bootargs = "earlycon=uart8250,mmio32,0xf0000000,115200n8"; + stdout-path = &uart0; .. But I don't see earlycon working with paramless earlycon - bootargs = "earlycon=uart8250,mmio32,0xf0000000,115200n8"; + bootargs = "earlycon"; stdout-path = &uart0; And I don't see how it would work for others as of 4.1-rc6 Relevant config items I have are: CONFIG_SERIAL_EARLYCON=y CONFIG_SERIAL_8250=y CONFIG_SERIAL_8250_CONSOLE=y CONFIG_SERIAL_CORE=y CONFIG_SERIAL_CORE_CONSOLE=y CONFIG_SERIAL_OF_PLATFORM=y ... There are 2 earlyparam handlers for earlcon, (1) param_setup_earlycon() -> setup_earlycon() -> register_console() (2) setup_of_earlycon() -> early_init_dt_scan_chosen_serial -> of_setup_earlycon() #1 only works when arg to earlycon is *not NULL* #2 only works when arg is *NULL*. For my case, #2 bails out early as __earlycon_of_table happens to be empty. 8071d8a0 T __earlycon_of_table 8071d8a0 000000c4 t __earlycon_of_table_sentinel This make sense since I don't see any OF_EARLYCON_DECLARE() in 8250 driver. As a quick hack I added one in 8250/8250_early.c @@ -152,3 +154,4 @@ static int __init early_serial8250_setup(struct earlycon_device *device, } EARLYCON_DECLARE(uart8250, early_serial8250_setup); EARLYCON_DECLARE(uart, early_serial8250_setup); +OF_EARLYCON_DECLARE(uart8250, "ns8250", early_serial8250_setup); I needed another fine adjustment as of_setup_earlycon() assumes mmio, while it needs to be memio32 for my case. @@ -199,7 +199,7 @@ int __init of_setup_earlycon(unsigned long addr, int err; struct uart_port *port = &early_console_dev.port; - port->iotype = UPIO_MEM; + port->iotype = UPIO_MEM32; With this paramless earlycon works. Now both the above are hacks, but I want to understand if I'm missing something in ARC port or does core need some adjustments along the lines of above, since presumably others have it working ! P.S. with respect to the original patch, I would fold it into for-next with change to stdout-path and keep earlycon as before - we can fix it up later. Thx, -vineet -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html