On 10/21/2015 04:21 AM, Masahiro Yamada wrote: > Hi. > > > > > I think there are three places where console could be enabled. > > [1] earlycon > > Each driver entry is declared with > EARLYCON_DECLARE() or OF_EARLYCON_DECLARE() > > > > [2] console_init() > > Each entry is declared with console_initcall() > > > > [3] when driver is probed > The console is usually enabled at this point > unless some special treatment is done. > > > > > My question is about [2]. For 8250 sub-drivers, the console_initcall() is only for legacy platforms, and not for 8250 ports added via serial8250_register_8250_port(). In this contexts, legacy platforms are: 1. early_serial_setup() 2. platforms that define SERIAL_PORT_DFNS (eg., ISA ports) At the point where console_initcall() occurs, the 8250 core has _not_ been initialized (ie., serial8250_init() has _not_ run). > I am using 8250-ish UART device. > > > I noticed univ8250_console_match() and univ8250_console_setup() > always fail at the point of [2] unless early_serial_setup() has been > called in advance; > however, it looks like early_serial_setup() is only used for old platforms. > > So, console cannot be enabled at [2] for modern platforms. Since console_init() => console_initcall() occurs before almost everything, it's not practical to use for probed drivers. > My questions are: > > - Given that earlycon can be now available for major architectures such ARM, > [2] will be deprecated at some point in the future? PPC and x86 platforms still rely on console_init() so it will be some time before this disappears. > - I am implementing earlycon for my own UART driver. > Is it meaningless to implement console_initcall() as well as earlycon? Probed drivers should only implement earlycon and console. 8250 sub-drivers should only implement earlycon and/or console if the base 8250 earlycon and/or console are not operational. Regards, Peter Hurley -- 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
