Hello, On Thu, 27 Jun 2019 19:58:17 +0900 Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > 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. I've confirmed that grub-x86 doesn't support devicetree option. I tried to add it, and tested it. https://github.com/mhiramat/grub/commit/644c35bfd2d18c772cc353b74215344f8264923a This works if there is ACPI, if it includes /chosen/linux,ftrace node only. (Anyway, we don't need other nodes on x86) At this moment, grub doesn't support DT overlay, so on arm/arm64 user must decompile DTB, add linux,ftrace node for tracing and compile it again. But if it supports overlay, I think we can give an overlay for tracer setting on boot up, that will be handy on arm/arm64 too. :) Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
