On Tuesday 02 September 2014 08:20:53 Rob Herring wrote: > >> > >> This alone is not okay. There is no such implementation of hardware. > > > > But the SBSA explicitly allows this. I don't know of any vendor who just > > implements the subset, but I've been told that this has been asked for. > > To use baudrate as an example, that must be configurable somehow > either with pl011 registers or in a vendor specific way. I suppose you > could do an actual implementation with all those things hardcoded in > the design, but that seems unlikely. Why does the baudrate need to be configurable? I think it's completely reasonable to specify a console port that has a fixed (as in the OS must not care) rate, and that can be implemented either as a UART with a programmable rate or as a set of registers that directly talks to a remote system management device over whatever hardware protocol they choose. > >> The DT must specify the implementation such as pl011. > > > > If it is a full featured PL011: sure. Then we don't need this driver at > > all and just use the SBSA UART spec as a guideline for our earlycon > > implementation. > > I will try to learn if there is someone actually implementing only the > > subset. > > I would have assumed you knew someone is. Otherwise, I don't really > think anything should be implemented at this point. Perhaps adding > SBSA uart as an explicit earlycon option would be worthwhile. Also, we > should consider using ttySx instead of ttyAMAx for SBSA compliant > systems (including ones with pl011). What about systems that have both a SBSA debug port and a 8250 compatible UART? That sounds like a very realistic hardware design choice for someone coming from an older x86/powerpc/mips/... chip that has 8250 and adds the extra port for SBSA compliance. Arnd -- 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
