Hi Arnd, 2015-10-21 18:19 GMT+09:00 Arnd Bergmann <arnd@xxxxxxxx>: > On Wednesday 21 October 2015 18:09:33 Masahiro Yamada wrote: >> Hi Arnd, >> >> >> 2015-10-21 17:57 GMT+09:00 Arnd Bergmann <arnd@xxxxxxxx>: >> > On Wednesday 21 October 2015 17:21:07 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]. >> >> >> >> 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. >> >> >> >> >> >> 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? >> >> >> >> - I am implementing earlycon for my own UART driver. >> >> Is it meaningless to implement console_initcall() as well as earlycon? >> > >> > I would still do both. We don't enable earlycon by default at the moment, >> > and I'd say things should remain working with just console_initcall(). >> > >> > How closely related to 8250 is your hardware? If it's not all that different, >> > you should probably reuse the existing driver. >> >> >> Very close. >> It is already in the mainline. >> >> drivers/tty/serial/8250/8250_uniphier.c >> >> The core parts are shared with 8250_core.c > > Ok, but I guess no close enough that it makes sense to use drivers/serial/of_serial.c Right. > >> I am trying to implement OF_EARLYCON_DECLARE() for that. >> >> I was just wondering if console_initcall() should work as well. >> >> >> As I said, I noticed the console_initcall() in 8250_core.c >> only works on very limited platforms. > > It works with all those that use of_serial.c, right? I doubt it. I have a board with a pure 8250-compat device working. ( compatible = "ns16550a") It uses of_serial.c, of course. As far as I tested, it would never enable the console at console_init(). The console is enabled when the UART driver is probed. (or earlycon if "earlycon" is specified in the kernel-parameter.) -- Best Regards Masahiro Yamada -- 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
