Hi Wolfram, On Monday 10 March 2014 13:38:37 Wolfram Sang wrote: > > I've recently reviewed a patch adding serial port aliases to the device > > tree and would like to pick your brains about a disagreement I had with > > the developer. > > And here is the developer :) > > > 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. > > First, I don't think this is restricted to serial ports but how to use > aliases in general. We may decide this or that way, yet we should do it > consistently. Using aliases this way for serial ports and that way for > I2C busses will create a mess. > And currently, I only know of 1:1 mappings for I2C/SPI. So, on the same > board, you'll need to open /dev/i2c-2, not /dev/i2c-0. > > From my experience, things get complicated when stuff gets added and the > numbers go wild: > > serial0 = &scif2; > serial1 = &scif3; > serial2 = &scif6; > serial3 = &scif0; > serial4 = &scif7; > > When debugging here, trying to remember which port to open for the > terminal, and which number to scan for in the schematics is error-prone > and a PITA. > > Yeah, the drawback is that the console might be at different places > across boards. I suggest to update inittab at runtime anyhow, since not > only the number but also the naming often changes (ttyXYZ to ttyABC). Just out of curiosity (as I could use it), do you have a sample implementation of dynamic inittab updates ? -- Regards, Laurent Pinchart
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