On Fri, Nov 9, 2012 at 11:23 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: > On 11/09/2012 09:28 AM, Grant Likely wrote: >> On Tue, Nov 6, 2012 at 10:37 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: > ... >>> I do rather suspect this use-case is quite common. NVIDIA certainly has >>> a bunch of development boards with pluggable >>> PMIC/audio/WiFi/display/..., and I believe there's some ability to >>> re-use the pluggable components with a variety of base-boards. >>> >>> Given people within NVIDIA started talking about this recently, I asked >>> them to enumerate all the boards we have that support pluggable >>> components, and how common it is that some boards support being plugged >>> into different main boards. I don't know when that enumeration will >>> complete (or even start) but hopefully I can provide some feedback on >>> how common the use-case is for us once it's done. >> >> From your perspective, is it important to use the exact same .dtb >> overlays for those add-on boards, or is it okay to have a separate >> build of the overlay for each base tree? > > I certainly think it'd be extremely beneficial to use the exact same > child board .dtb with arbitrary base boards. > > Consider something like the Arduino shield connector format, which I > /believe/ has been re-used across a wide variety of Arduino boards and > other compatible or imitation boards. Now consider a vendor of an > Arduino shield. The shield vendor probably wants to publish a single > .dtb file that works for users irrespective of which board they're using > it with. > > (Well, I'm not sure that Arduino can run Linux; perhaps that's why you > picked BeagleBone capes for your document!) Correct, the Arduino is only an AVR with a tiny amount of ram. No Linux there. However, Arduino shields are a good example of a use case. I think there are even some Arduino shield compatible Linux boards out there. > I suppose it would be acceptable for the shield vendor to ship the .dts > file rather than the .dtb, and hence need to build the shield .dtb for a > specific base board. That would be better I think than relying on a binary. However, some though needs to go into how to handle base boards that /aren't/ mostly equivalent. Such as if they have a different GPIO controller. It may be that for gpios and irqs, the solution really is to use interrupt-map and create a gpio-map. i2c, spi and others still would need to become children of the correct bus. > However, I think the process for an end-user needs to be as simple as > "drop this .dts/.dtb file into some standard directory", and I imagine > it'll be much easier for distros/... to make that process work if > they're dealing with a .dtb that they can just blast into the kernel's > firmware loader interface, rather than having to also locate the > base-board .dts/.dtb file, and run dtc and/or other tools on both .dts > files together. The base-board .dts is unnecessary. dtc is fully capable of using /proc/device-tree as the source material. :-) g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. -- 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
