From mboxrd@z Thu Jan 1 00:00:00 1970 MIME-Version: 1.0 Date: Tue, 2 Jul 2019 07:30:57 -0600 References: <156113387975.28344.16009584175308192243.stgit@devnote2> <20190627195817.211ab4bea422f37e539e47e8@kernel.org> <20190702184730.b0247eb780ffa48d40a61a81@kernel.org> In-Reply-To: <20190702184730.b0247eb780ffa48d40a61a81@kernel.org> Message-ID: Subject: Re: [RFC PATCH 00/11] tracing: of: Boot time tracing using devicetree From: Rob Herring Content-Type: text/plain; charset="UTF-8" To: Masami Hiramatsu Cc: Steven Rostedt , Frank Rowand , Tom Zanussi , Ingo Molnar , Namhyung Kim , Jiri Olsa , Arnaldo Carvalho de Melo , "linux-kernel@vger.kernel.org" , devicetree@vger.kernel.org List-ID: On Tue, Jul 2, 2019 at 3:47 AM Masami Hiramatsu wrote: > > Hello, > > On Thu, 27 Jun 2019 19:58:17 +0900 > Masami Hiramatsu wrote: > > > Hi Rob, > > > > On Wed, 26 Jun 2019 15:58:50 -0600 > > Rob Herring wrote: > > > > > On Fri, Jun 21, 2019 at 10:18 AM Masami Hiramatsu 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