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. The DT support won't be all that quick to implement. The challenge with the DT parsing is we have to do it on the flattened DT. I have something functioning, but it doesn't do any address translation which is the hard part. Rob -- 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
