On Wed, May 7, 2014 at 10:47 AM, Eric Nelson <eric.nelson@xxxxxxxxxxxxxxxxxxx> wrote: > Hi Olof, > > > On 05/07/2014 10:24 AM, Olof Johansson wrote: >> >> Hi, >> >> On Wed, May 7, 2014 at 10:12 AM, Eric Nelson >> <eric.nelson@xxxxxxxxxxxxxxxxxxx> wrote: >>> >>> Hi all, >>> >>> I suspect that this has been discussed previously, but I'm a >>> N00b to DT and Google hasn't helped identify a discussion >>> on the list. >>> >>> While getting my feet wet with DTS, I was quite surprised to >>> see that there's no support for making parts of DTS files >>> conditional on the kernel configuration. >>> >>> We often cost-optimize BOMs for our standard boards and omit >>> bits and pieces not needed for a particular build, and >>> it would be nice to surround optional components with >>> conditionals: >>> >>> #ifdef CONFIG_BLAH >>> #endif >>> >>> Please advise, >> >> >> The DTS is independent on what drivers the kernel is actually >> enabling. It should focus on what is actually there on hardware, and >> not what is enabled in software. >> >> I think I know where you're coming from on this -- on some board-file >> setups people used to not register the platform_device if the driver >> wasn't configured. That was also not really a good way to do it, but >> it made a bit more sense there, since you'd save the few bytes used by >> the platform_device/platform_data structures. >> > > It's not a question of space, but functionality. > > We had this come up recently when optimizing a BOM for use > without Wi-Fi. If we omit the device and associated buffers, > the SDIO lines are left floating, so the detection code will > complain. > > It seems reasonable to tell the kernel to skip this if the > WiFi driver isn't configured into the kernel (i.e. there's > no point in enumerating), so I was hoping to surround this > USDHC2 block with #ifdefs: > > > https://github.com/boundarydevices/linux-imx6/blob/boundary-imx_3.10.17_1.0.0_ga/arch/arm/boot/dts/imx6qdl-nitrogen6x.dtsi#L640 > > The alternative aren't very nice: > populate extra parts to drive these signals, or > copy the DTB and strip out the unused parts > > The first is wasteful (and environmentally un-friendly), and > the second doesn't scale very well and pollutes the Git tree. > > Prior to DT, we surrounded the device startup calls with #ifdefs > like this: > > https://github.com/boundarydevices/linux-imx6/blob/boundary-jb4.3_1.0.0-ga/arch/arm/mach-mx6/board-mx6_nitrogen6x.c#L1409 It is really annoying that you can't include a DTS in another DTS (only DTSIs). This is a major shortcoming of the tools, as far as I am concerned. So, the best way we've found to do this is to create a shared dtsi that has practically everything in it, then a skeleton DTS for the "full" product, and a separate DTS for the cost-reduced version. The cost-reduced DTS would insert a status = "disabled"; for the sdio controller. That's a solution that scales very poorly as well, though. Best would be if a DTS could just include another DTS for minor updates, such as disabling the sdio controller in this case. I'm sure there were some language-puritan reasons for not allowing that though. Someone care to fill in the history? -Olof -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
