adding devicetree list, devicetree maintainers On 11/18/17 12:59, Ulf Samuelsson wrote: > I noticed when checking out the OpenWRT support for the board that they have a method to avoid having to pass the device tree address to the kernel, and can thus boot device tree based kernels with U-boots that > does not support device trees. > > Is this something that would be considered useful for including in mainstream: > > BACKGROUND: > Trying to load a yocto kernel into a MIPS target (MT7620A based), > and the U-Boot is more than stupid. > Does not support the "run" command as an example. > They modified the U-Boot MAGIC Word to complicate things. > The U-Boot is not configured to use device tree files. > The board runs a 2.6 kernel right now. > > Several attempts by me a and others to rebuild U-Boot according to the H/W vendors source code and build instructions results in a bricked unit. Bricked units cannot be recovered. > > Not my choice of H/W, so I cannot change it. > > > =================================================================== > OPENWRT: > I noticed when checking out the OpenWRT support for the board that they have a method to avoid having to pass the device tree address to the kernel, and can thus boot device tree based kernels with U-boots that > does not support device trees. > > What they do is to reserve 16 kB of kernel space, and tag it with an ASCII string "OWRTDTB:". > After the kernel and dtb is built, a utility "patch-dtb" will update the vmlinux binary, copying in the device tree file. > > =================================================================== > It would be useful to me, and I could of course patch the mainstream kernel, but first I would like to check if this is of interest for mainstream. > > I envisage the support would look something like: > > ============ > Kconfig. > config MIPS > select HAVE_IMAGE_DTB > > config HAVE_IMAGE_DTB > bool > > if HAVE_IMAGE_DTB > config IMAGE_DTB > bool "Allocated space for DTB within image > > config DTB_SIZE > int "DTB space (kB) > > config DTB_TAG > string "DTB space tag" > default "OWRTDTB:" > endif > > ============ > Some Makefile > obj-$(CONFIG_INCLUDE_DTB) += image_dtb.o > > ============ > image_dtb.S: > .text > .align 5 > .ascii CONFIG_DTB_TAG > EXPORT(__image_dtb) > .fill DTB_SIZE * 1024 > > =================== > arch/mips/xxx/of.c: > > #if defined(CONFIG_IMAGE_DTB) > if (<conditions to boot from dtb_space>) > __dt_setup_arch(__dtb_start); > else > __dt_setup_arch(&__image_dtb); > #else > __dt_setup_arch(__dtb_start); > #endif > > I imagine that if the support is enabled for a target, it should > be possible to override it with a CMDLINE argument > > > They do something similar for the CMDLINE; copying it into the vmlinux, to allow a smaller boot > > > -- 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
