On Sat, 22 Mar 2014 09:14:31 -0500, Rob Herring <robherring2@xxxxxxxxx> wrote: > On Sat, Mar 22, 2014 at 4:54 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Friday 21 March 2014, Rob Herring wrote: > >> From: Rob Herring <robh@xxxxxxxxxx> > >> > >> This started out as an attempt to add arm64's earlyprintk support to ARM > >> in order to get an earlier, runtime setup console on multi-platform > >> kernels. The first issue was needing the fixmap support which > >> conveniently Mark Salter was working on and is mostly in place now. Like > >> many things on ARM and arm64 now, it then became where do I put the now > >> common, shared code. After digging more into various early console/printk > >> support, it turns out the 8250_early.c setup code was the best starting > >> point. > >> > >> This is based on Mark Salter's fixmap support currently in linux-next. > >> This is tested on arm64 and ARM with pl011 and 8250. The ARM support > >> also requires fixmap and fixed mapping support which are not yet in place. > >> I have some patches in my tree to support fixmap, but they need some more > >> work. Fortunately, once fixmap is in place, it is just a Kconfig option > >> to enable earlycon support on ARM. A git tree is available here[1]. > >> > >> Based on this series, I would like to add support for doing earlycon > >> setup using DT. > > > > Hi Rob, > > > > I like this series a lot, great work! > > > > I would consider the DT parsing support essential here, we should not > > merge the patches until that is done as well, because I don't want > > to see users pass earlycon command line options in DT when they can > > use the established "linux,stdout-path" property instead. I would > > expect that in almost every case in which we are booting using DT > > today, we can just use linux,stdout-path to locate the device that > > the boot loader has already set up and start usign it. > > I think this series stands on its own. It is largely refactoring > existing code and supporting existing command line options (arm64 just > changes from earlyprintk= to earlycon=). There will be cases where > changing the kernel command line is the only way to setup the > earlycon. Also, I think we would still want the kernel command line to > control whether or not we enable the earlycon (i.e. earlycon=dt). > There's not a standard way for how bootloaders would decide to set > "linux,stdout-path" or not. I agree. I really like this series and I don't think it needs to wait for DT parsing. Another issue is that the earlycon assumes the port is already set up, but the /chosen/stdout-path binding doesn't guarantee that. We'll have to make sure the kernel knows when it is valid to use /chosen/stdout-path before enabling an early console. g. -- 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
