On 06/15/13 15:14, Grant Likely wrote: > On Wed, 12 Jun 2013 21:12:39 +0200, Walter Goossens <waltergooss...@home.nl> > wrote: >> On 06/12/13 20:23, Grant Likely wrote: >>> On Wed, Jun 12, 2013 at 6:33 PM, Collins, Rod >>> <rod.coll...@saabsensis.com> wrote: >>>> The blob is built into the zImage.initramfs.gz image which is put into >>>> flash. The zImage.initramfs.gz is self copied from flash to RAM, then >>>> uncompressed to the running area. I will dig into the location of the >>>> blob in the image and report back. >>> Thanks. If it is appended to the zImage wrapper, then things should be >>> fine (this is the expected way to do when not passed in from the >>> bootloader). If a *.dtb.o target has been used to embedded it into the >>> kernel-proper (vmlinux) then you will have a problem. The *.dtb.S >>> target puts the dtb data into the dtb.init.rodata section which gets >>> discarded. >>> >>> g. >> Hi Grant, >> >> you're right that's exactly what nios2 is doing... >> I guess we could modify the section where it gets loaded but that sounds >> to me a bit like a hack... What is the best target to look at for a >> clean, similar solution? Arm with CONFIG_ARM_APPENDED_DTB? > My first recommendation would be the way it is described in > Documentation/arm/Booting and Documentation/devicetree/booting-without-of.txt, > by which I mean passing the dtb into the kernel from the bootloader. > This is the preferred approach on both PowerPC and ARM, but I do > undertstand that doesn't work in all situations; such as if there is no > bootloader. Nios2 also supports passing a devicetree through u-boot if I'm not mistaken. > The second choice is to attach it to the kernel image as a > post-processing step. On ARM that is enabled by CONFIG_ARM_APPENDED_DTB > which makes it possible to merely dd the DTB onto the end of the kernel > image. PowerPC uses a slighly different approach where a script takes > care of linking the DTB into the bootwrapper. See the > arch/powerpc/boot/wrapper script for details. dd-ing the dtb onto the end sounds nice. > Either way, I don't think it is a good architectural decision to link > the dtb directly into the kernel proper because doing so precludes ever > having a single kernel image bootable on multiple platforms. On an FPGA > platform it is particularly useful not having to rebuild the kernel > every time the FPGA design changes. Yes I know, it's just one of the supported ways of passing the devicetree. It's just easier to explain to new users who might not have much experience with linux/uboot. Thanks for all the advice!
Walter > g. > > _______________________________________________ devicetree-discuss mailing list devicetree-discuss@lists.ozlabs.org https://lists.ozlabs.org/listinfo/devicetree-discuss
