From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Subject: Re: [RFC PATCH 00/11] tracing: of: Boot time tracing using devicetree Date: Tue, 2 Jul 2019 18:47:30 +0900 Message-ID: <20190702184730.b0247eb780ffa48d40a61a81@kernel.org> References: <156113387975.28344.16009584175308192243.stgit@devnote2> <20190627195817.211ab4bea422f37e539e47e8@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190627195817.211ab4bea422f37e539e47e8@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: Masami Hiramatsu Cc: Rob Herring , 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: devicetree@vger.kernel.org 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