On 09/06/2019 08:59, Chris Johns wrote: > On 9/6/19 4:29 pm, Vijay Kumar Banerjee wrote: >> On Sun, Jun 9, 2019 at 6:22 AM Chris Johns <chr...@rtems.org >> <mailto:chr...@rtems.org>> wrote: >> On 8/6/19 5:58 pm, Christian Mauderer wrote: >> > ----- Ursprüngliche Mail ----- >> >> Von: "Oyake, Amalaye (386M)" <amalaye.oy...@jpl.nasa.gov >> <mailto:amalaye.oy...@jpl.nasa.gov>> >> >> An: "Chris Johns" <chr...@rtems.org <mailto:chr...@rtems.org>>, "Vijay >> Kumar Banerjee" <vijaykumar9...@gmail.com >> <mailto:vijaykumar9...@gmail.com>>, "Christian Mauderer" >> >> <christian.maude...@embedded-brains.de >> <mailto:christian.maude...@embedded-brains.de>> >> >> CC: "RTEMS Users" <users@rtems.org <mailto:users@rtems.org>> >> >> Gesendet: Samstag, 8. Juni 2019 04:57:02 >> >> Betreff: Re: [EXTERNAL] Re: BeagleBone Black Networking (wifi and/or >> wired) >> > >> >> Device Tree overays are a method used to update the Device Tree. >> Given a >> device >> >> tree that describes all the devices, let's say you add a new SPI >> device, you >> >> can update the device tree with a (blob) device tree overlay. >> >> >> >> I should ask (without Googling), What is the Device Tree Overlay >> mechanism in >> >> RTEMS? >> > >> > >> > Hello Amalaye, >> > >> > as far as I know, the device tree overlay mechanism in RTEMS is not >> implemented. There is the prototype of fdt_overlay_apply() in libfdt.h >> but >> there is no implementation. So there are two methods: >> > >> > 1. Applying the overlay on a build machine. Vijay did that during his >> tests. >> >> How do you do this? >> >> I used `fdtoverlay` from libfdt on linux host. > > Could cpukit/dtc/libfd in RTEMS be updated to support this code? I see > freebsd's > kernel has the code. >
Theoretically that could be possible. If I understand it correctly, that would mean that we could apply an overlay after boot. That would mean a lot of additional stuff. For all changed parts the matching drivers would have to be load or maybe some other ones have to be unload. Basically we would need a dynamic device management for that. As long as there is no concrete use case I don't think it's useful to do that work. >> >> > 2. Use the U-Boot mechanism to apply overlays before booting RTEMS. >> That >> should most likely work too. But I didn't test it yet. >> >> OK >> >> >> On 6/7/19, 6:17 PM, "users on behalf of Chris Johns" >> <users-boun...@rtems.org <mailto:users-boun...@rtems.org> on >> >> behalf of chr...@rtems.org <mailto:chr...@rtems.org>> wrote: >> >> >> >> On 8/6/19 1:53 am, Vijay Kumar Banerjee wrote: >> >> > >> >> > I would like to add that in two projects of this year( I2C and >> PRU-ICSS drivers) >> >> > we >> >> > are using our own device tree overlays that make our drivers >> work. >> Where to add >> >> > the device >> >> > tree related stuff seems like an important question. >> >> >> >> What are device tree overlays? >> > >> > Like Oyake already said: They are some small pices of device trees that >> are just added to the base tree in it's binary form. Linux (and most >> likely >> FreeBSD too) supports that even after boot. If you add an overlay it >> re-parses the device tree, updates GPIO settings and loads new drivers. >> The >> alternative is to let the boot loader apply them during boot. >> >> What is needed to do this? Maybe I can add it to rtems-boot-image as a >> way to >> handle this at the u-boot version. >> >> I have also tried to automate it by adding it in uEnv.txt as a script, it >> worked >> nicely to apply >> the overlay on the blob, I haven't tested it with any app though, but the >> overlay applied >> successfully. Here's what the test uEnv.txt looks like. >> ``` >> setenv bootdelay 5 >> uenvcmd=run overlay_cmd boot >> overlay_cmd=fatload mmc 0 0x80800000 rtems-app.img; fatload mmc 0 0x88000000 >> am335x-boneblack.dtb; fatload mmc 0 0x88100000 am335x-rtems.dtbo; fdt addr >> 0x88000000; fdt resize 0x1000; fdt apply 0x88100000; >> boot=bootm 0x80800000 - 0x88000000; >> ``` >> >> You can add something like this to the uEnv.txt in SD card image. In the >> above >> script >> the am335x-boneblack.dtb is the one from linux and am335x-rtems.dtbo is >> generated >> with dtc from the overlay written by me. > > Ah I see. I think this could be added to rtems-boot-image. There is something > attractive about building the fdt at run time on the board from the needed > pieces. If you try to do a more general purpose approach it could be worth having a look at the boot sequences done on boards like the Beagle or Raspberry. As far as I know they have sequences that just apply all overlays from a directory. Best regards Christian > > Chris > _______________________________________________ > users mailing list > users@rtems.org > http://lists.rtems.org/mailman/listinfo/users > _______________________________________________ users mailing list users@rtems.org http://lists.rtems.org/mailman/listinfo/users
