Hi Rob, On Wed, 26 Jun 2019 15:58:50 -0600 Rob Herring <robh+dt@xxxxxxxxxx> wrote: > On Fri, Jun 21, 2019 at 10:18 AM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > > Hi, > > > > Here is an RFC series of patches to add boot-time tracing using > > devicetree. > > > > Currently, kernel support boot-time tracing using kernel command-line > > parameters. But that is very limited because of limited expressions > > and limited length of command line. Recently, useful features like > > histogram, synthetic events, etc. are being added to ftrace, but it is > > clear that we can not expand command-line options to support these > > features. > > > > Hoever, I've found that there is a devicetree which can pass more > > structured commands to kernel at boot time :) The devicetree is usually > > used for dscribing hardware configuration, but I think we can expand it > > for software configuration too (e.g. AOSP and OPTEE already introduced > > firmware node.) Also, grub and qemu already supports loading devicetree, > > so we can use it not only on embedded devices but also on x86 PC too. > > Do the x86 versions of grub, qemu, EFI, any other bootloader actually > enable DT support? I didn't think so. Certainly, an x86 kernel doesn't > normally (other than OLPC and ce4100) have a defined way to even pass > a dtb from the bootloader to the kernel and the kernel doesn't > unflatten the dtb. Sorry, the grub part, I just found this entry. I need to check this can work on x86 too. https://www.gnu.org/software/grub/manual/grub/html_node/devicetree.html Anyway, I've tested this series on qemu-x86 with --dtb option. The kernel boot with ACPI and DT (hardware drivers seem initialized by ACPI), and it seems unflatten the dtb correctly. > > For arm64, the bootloader to kernel interface is DT even for ACPI > based systems. So unlike Frank, I'm not completely against DT being > the interface, but it's hardly universal across architectures and > something like this should be. Neither making DT the universal kernel > boot interface nor creating some new channel as Frank suggested seems > like an easy task. I don't want it making this for all architectures but an option for architecutres which supports DT already... Thank you, > > Rob -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
