On 05/07/2015 06:25 PM, Maciej W. Rozycki wrote: > On Thu, 7 May 2015, Peter Hurley wrote: > >>> How does this overload interact with multiple `console=' options being >>> present BTW, which one is considered the early console? Or do we support >>> driving multiple early consoles in parallel just as we do with regular >>> consoles? >> >> Please familiarize yourself with the existing 'console=' and 'earlycon=' >> command line options documented in Documentation/kernel-parameters.txt > > Thank you for your suggestion, however that documentation does not answer > my questions I am afraid (and neither does serial-console.txt). Otherwise > I wouldn't have asked them in the first place. If you don't know the > answers either, then it's OK to say: "I don't know". > > E.g. (given the parameter aliasing we have) will: > > `earlycon=uart8250,io,0x3f8 console=tty0' > `console=tty0 earlycon=uart8250,io,0x3f8' > > do what I expect it to, that is open the UART at 0x3f8 as an early console > and then hand it over to the ttyS0 device as respectively a secondary and > the primary (/dev/console) regular console? No. >From Documentation/kernel-parameters.txt: earlycon= [KNL] Output early console device and options. ..... uart[8250],io,<addr>[,options] uart[8250],mmio,<addr>[,options] uart[8250],mmio32,<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address. MMIO inter-register address stride is either 8-bit (mmio) or 32-bit (mmio32). The options are the same as for ttyS, above. IOW, command line parameters of the form: earlycon=uart8250,... does not perform earlycon-to-console handoff. Also from Documentation/kernel-parameters.txt: console= [KNL] Output console device and options. ..... uart[8250],io,<addr>[,options] uart[8250],mmio,<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address, switching to the matching ttyS device later. The options are the same as for ttyS, above. IOW, command line parameters of the form: console=uart8250,... performs earlycon-to-console handoff. Furthermore, because of the way aliasing was implemented in 2007, it has been possible since to start _any_ earlycon with command line parameters of the form: console=<earlycon name>,.... However, only 8250 implemented the console handoff. 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
