lkml.org 
[lkml]   [2019]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC PATCH 00/11] tracing: of: Boot time tracing using devicetree
    Hi Rob,

    On Wed, 26 Jun 2019 15:58:50 -0600
    Rob Herring <robh+dt@kernel.org> wrote:

    > On Fri, Jun 21, 2019 at 10:18 AM Masami Hiramatsu <mhiramat@kernel.org> 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@kernel.org>

    \
     
     \ /
      Last update: 2019-06-27 12:59    [W:3.105 / U:0.336 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site