Hi Rob, On Thursday 27 March 2014 08:54:09 Rob Herring wrote: > On Thu, Mar 27, 2014 at 7:50 AM, Laurent Pinchart wrote: > > Hello DT maintainers, > > > > Ping ? This issue is blocking the merge of serial port DT support on > > Renesas platforms, as we need to decide on how to name the ports. > > This seems like a topic for devicetree-spec. Indeed. > > On Tuesday 11 March 2014 12:57:59 Laurent Pinchart wrote: > >> On Monday 10 March 2014 13:57:23 Arnd Bergmann wrote: > >> > On Monday 10 March 2014 12:59:03 Laurent Pinchart wrote: > >> > > The SoC includes 8 serial ports. They are all disabled in the SoC > >> > > .dtsi, and enabled selectively by board DT files. As not all serial > >> > > ports are available on all boards, the question was whether to add > >> > > aliases for all ports (in the .dtsi in this case) like > >> > > > >> > > serial0 = &scif0; > >> > > serial1 = &scif1; > >> > > serial2 = &scif2; > >> > > serial3 = &scif3; > >> > > serial4 = &scif4; > >> > > serial5 = &scif5; > >> > > serial6 = &scif6; > >> > > serial7 = &scif7; > >> > > > >> > > or to just add aliases for the enabled ports (in the board DT file) > >> > > like > >> > > > >> > > serial0 = &scif2; > >> > > serial1 = &scif3; > >> > > > >> > > Note the numbering in the latter case: as the board doesn't use > >> > > serial ports 0 and 1, hardware ports 2 and 3 become logical ports 0 > >> > > and 1. > >> > > > >> > > I considered that having Linux create ttySC0 and ttySC1 devices for > >> > > the first two ports of the board, regardless of which hardware ports > >> > > are used, is simpler from a user point of view (it allows sharing the > >> > > same inittab settings for the console serial port across several > >> > > boards for instance). I'd appreciate feedback on that. > >> > > >> > I think the traditional interpretation is that we want to use the > >> > aliases to reflect the device names in the OS. > >> > >> If I interpret this correctly it means that the question boils down to > >> whether we want the system to expose ttySC0 and ttySC1 or ttySC2 and > >> ttySC3, in case only ports 2 and 3 are enabled. > >> > >> Let's note that, despite the above example showing 8 instances of > >> identical serial IP cores, the reality is a bit more complex and Renesas > >> SoCs usually include different serial IP cores with several instances of > >> each of them. Ports of the same time are numbered in the datasheet, but > >> there's no standard or natural ordering global to all serial ports. > >> > >> This starts to remind me about the whole stable network device name > >> changes we went through recently. > >> > >> > This however comes back to the more general issue of serial port device > >> > naming: Linux traditionally uses separate names per driver (e.g. ttySC0 > >> > instead of ttyS0). > >> > > >> > There has been discussion in the past about changing this to let all > >> > drivers use the same namespace, but it's not yet clear to me how we'd > >> > do this in a 100% backwards compatible way. Maybe it's best left to > >> > udev to figure out the driver independent name, but then we definitely > >> > should use the alias for that name. > > This discussion has come up in just the last month or so. > > My opinion is device name numbering should start at 0 with 0 being the > preferred console device. My main reasoning is giving consistent naming > across boards and it is more inline with how other devices are named. The > aliases are just to give you consistency in the numbering within the 0 to N. > Hopefully this is inline with what other platforms have done as above all I > think we should be consistent. That's my preference as well, but not everybody agreed, hence the RFC. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe devicetree-spec" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
