11:04 <baltazar> hi! I'm using a nanopi neo (allwinner h3 based), and I'm not sure how to enable uart1 and uart2.

11:04 <baltazar> am I supposed to create a device tree overlay?

11:04 <gamiee> baltazar: if your OS supports that, then yes. Else you need to modify device tree

11:04 <baltazar> if so, how is that done?

11:05 <baltazar> gamiee: I assume linux supports them

11:06 <gamiee> Sorry, I meant distribution

11:06 <baltazar> oh, well, I'm not sure. I'm on archlinuxarm

11:07 <gamiee> No idea about archlinuxarm if it supports dt overlays. Then modifying the device tree is best bet

11:09 <baltazar> is dt support really distro dependent?

11:09 <gamiee> dt overlay, yes

11:11 <baltazar> alright, thanks

11:11 <gamiee> Or I might be wrong

11:12 <baltazar> welp

11:12 <gamiee> I was working with it very long time ago, but as far as I remember, in Armbian, it works by way that u-boot applies dt overlays into final device tree, which is afterwards loaded by kernel.

11:13 <gamiee> Anyway, if you want to enable uart1 and uart2, just decompile current used .dtb to .dts, and enable them.

11:13 <gamiee> and again convert it back to dtb

11:13 <baltazar> yeah, well I tried applying it from u-boot, but it didn't work (can't remember the exact error)

11:15 <baltazar> I mean, I might have messed up the overlay itself, I really don't know how this is supposed to work

11:15 <baltazar> but this is what I have, based on how uart0 is enabled in the device tree sources: http://ix.io/3TvF

11:16 <gamiee> overlays are made bit differently

11:17 <gamiee> anyway, best is to just edit dtb directly

11:17 <baltazar> but that sounds like a pain to update

11:18 <baltazar> I mean, probably device trees don't get updated very often, but still

11:18 <gamiee> well, if you plan to make many changes (and you want to be able to enable / disable it between reboots), dt overlay is needed

11:19 <gamiee> https://u-boot.readthedocs.io/en/latest/usage/fdt_overlays.html this might be helpful

11:19 <gamiee> also this can explain it bit more: https://source.android.com/devices/architecture/dto

11:20 <baltazar> thanks!

11:20 <gamiee> No problem :)

11:20 <baltazar> hmm, well I looked at this before: https://www.kernel.org/doc/html/latest/devicetree/overlay-notes.html

11:21 <baltazar> and that's why I wrote my device tree overlay like I did, and if I compile it with dtc into a tdbo, printing it with dtc again shows something similar to the example in the u-boot docs you linked

11:23 <baltazar> this is the output of `dtc enable-uart.dtbo`: http://ix.io/3TvH

11:25 <baltazar> although I'm not sure why it has the actual references inside __fixups__ instead of having them in target or pinctrl-0

11:26 <baltazar> oh, apparently if I compile then dump the u-boot example it looks exactly like that; the references are moved to __fixups__

11:32 <baltazar> however, in u-boot, if I do `load ${devtype} ${devnum}:1 ${fdtoverlay_addr_r} ${bootdir}/enable-uart.dtbo` then `fdt apply ${fdtoverlay_addr_r}` it fails with the error `failed on fdt_overlay_apply(): FDT_ERR_NOTFOUND`

11:32 <gamiee> afk, will reply within 45 mins

11:52 <baltazar> bah, I based my thing on how uart0 was configured, but its pinctrl parameter is called &uart0_pa_pins, unlike uart1&2's which is called &uart1_pins and &uart2_pins

11:52 <baltazar> and I just blindly copied the config and only changed the number

11:53 <baltazar> now it applies successfully in u-boot

13:09 <gamiee> back

16:17 <apritzel> which brings up the question: should there be a repository for those rather common overlays?

16:17 <apritzel> and should we simplify applying them in U-Boot? Like: "apply all .dtbo files in this directory"

16:26 <gamiee> apritzel: I think simplified usage of overlays in u-boot would be amazing

17:42 <apritzel> gamiee: what about: fdt apply_all mmc 0:1 overlays

17:43 <apritzel> as in: fdt apply_all <ifname> <dev_part_str> [directory]

18:59 <baltazar> apritzel: yeah, that would simplify usage a lot

19:00 <baltazar> and yeah, an overlay repository would be pretty useful as well, but I'm not sure how generic you could make it. as I just learned, the naming of these references isn't very consistent

19:02 <baltazar> at least it would surely be useful for people like me who want to figure out how to create such an overlay. I couldn't really find any straightforward examples, I only managed to put this together based on that linux kernel docs page and the original device tree sources

19:36 <apritzel> baltazar: well, overlays are board specific, not only because of the references

19:38 <apritzel> or at least SoC specific, I guess

19:38 <baltazar> apritzel: well, I kinda imagine maintaining such a repo for every individual board would be close to impossible. not to say it wouldn't be cool tho

22:29 <jernej> gamiee: applying DT overlays is extremely simple, if you're using PXE boot

22:30 <jernej> you just list path to all overlays you want to apply in config file

22:31 <jernej> note, this DT overlay handling is custom U-Boot extension, so it's not portable

22:34 <jernej> while I see why would be mechanism to apply all overlays from specified directory useful in some cases, I think it's easier for distros to ship all board/soc specific overlays and you just list those that you want in some file

22:34 <jernej> we're using that in LE

22:59 <apritzel> jernej: too late ...

23:00 <apritzel> I implemented what I sketched above

23:01 <apritzel> not sure why this was there for PXE, but not for filesystems/block devices, which are probably more used

23:01 <apritzel> the plan would be to have a directory where users just drop the .dtbo files they want to have applied, and then:

23:04 <apritzel> fdt resize; fdt apply_all ${devtype} ${devnum}:${distro_bootpart} overlays