On 11/8/2012 3:28 AM, Koen Kooi wrote: > > Op 7 nov. 2012, om 23:35 heeft Ryan Mallon <rmallon@xxxxxxxxx> het volgende geschreven: > >> On 06/11/12 08:40, Tabi Timur-B04825 wrote: >>> On Mon, Nov 5, 2012 at 2:40 PM, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote: >>> >>>> Jane is building custom BeagleBone expansion boards called 'capes'. She >>>> can boot the system with a stock BeagleBoard device tree, but additional >>>> data is needed before a cape can be used. She could replace the FDT file >>>> used by U-Boot with one that contains the extra data, but she uses the >>>> same Linux system image regardless of the cape, and it is inconvenient >>>> to have to select a different device tree at boot time depending on the >>>> cape. >>> >>> What's wrong with having the boot loader detect the presence of the >>> Cape and update the device tree accordingly? We do this all the time >>> in U-Boot. Doing stuff like reading EEPROMs and testing for the >>> presence of hardware is easier in U-Boot than in Linux. >> >> This is probably okay for some hardware, but doesn't work in the general >> case. Not all hardware is detectable, for example a cape which just adds >> a set of LEDs for GPIO pins. Also, some hardware might not easily be >> detectable without adding additional complexity to the boot loader. > > And as Pantelis mentioned before, I really don't want my users to change the bootloader whenever they add a new LED. Touching the bootloader is just too accident prone, we had a ton of RMA requests for older versions of the beagleboard from people trying to upgrade u-boot. One possibility for dynamic device tree mods would be to run Open Firmware from u-boot and have it generate the device tree and possibly modify it either interactively or from a script loaded from a file or the network. OFW could then either load Linux directly or return to u-boot, which would proceed with loading. > > Apart from the above I'd like to have fewer points of failure. Right now I need to keep uImage and foo.dtb in sync and I hate to add u-boot to that equasion as well. > > regards, > > Koen > _______________________________________________ > devicetree-discuss mailing list > devicetree-discuss@xxxxxxxxxxxxxxxx > https://lists.ozlabs.org/listinfo/devicetree-discuss > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
