Messages in this thread | | | Subject | Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2) | From | Koen Kooi <> | Date | Thu, 8 Nov 2012 14:28:39 +0100 |
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Op 7 nov. 2012, om 23:35 heeft Ryan Mallon <rmallon@gmail.com> 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@secretlab.ca> 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.
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
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