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    Subject[RFC PATCH 0/2] device tree support for board revision
    Date
    Privously without using device trees system revision was carried over ATAGs.
    Now with device tree system revision information is not carried at all. This
    RFC proposes a method for this.

    With ARM arch system revision information (as 4 digit hex string) has been
    available in /proc/cpuinfo.

    Respective change is needed to boot loader to provide board revision. U-boot
    provides board_rev environment variable that holds string version of board
    revision information.

    With BeagleBone Black I was able to get following /proc/cpuinfo output:

    processor : 0
    model name : ARMv7 Processor rev 2 (v7l)
    BogoMIPS : 996.14
    Features : half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpd32
    CPU implementer : 0x41
    CPU architecture: 7
    CPU variant : 0x3
    CPU part : 0xc08
    CPU revision : 2

    Hardware : Generic AM33XX (Flattened Device Tree)
    Revision : 000B
    Serial : 1614BBBK1211

    Note: I set board_serial to serial# in u-boot to get serial number.

    Reason why I deviced to go RFC approach was that there is kinda definition
    problem here and possibilty that it might be a good idea to define more
    than one field to device tree. Also there seems to be multiple ways that
    people try to workaround the issues so it would be a good idea to
    standardize the interfaces a bit.

    One problem here is that what does actually those fields mean in
    /proc/cpuinfo?

    What does "Revision" mean? Does it mean board revision, device revision or
    system revision?

    Same goes for "Serial". Does it mean board serial, device serial or system
    serial?

    I see that "board" here would mean PCB or SoM module whose manufacturer
    defines model name, serial number and revision.

    Then we have "device" scope which I would see that it means PCB and chasis
    of the device, and in chasis you might have label with information like
    device model, serial number and revision. One device can consist of one or
    more boards.

    Then we have "system" scope which I would see that it means collection of
    devices. System might have model and serial number (haven't seen one with
    revision thou). It might be that "system" level is out-of-scope for device
    tree interface level.

    It may be that /proc/cpuinfo is wrong place to display this information but
    as a result of this discussion I would like to see the standard way to pass
    this information as it might be that bootloader can only access the
    information (in case of multipurpose pin in chip). And the standard way for
    user space to access this information.

    Thanks,
    Vesa Jääskeläinen

    Vesa Jääskeläinen (2):
    Documentation: devicetree: root node board-revision property
    documentation
    arm: setup: Show the board revision from devicetree in cpuinfo

    Documentation/devicetree/booting-without-of.txt | 1 +
    arch/arm/kernel/setup.c | 12 +++++++++++-
    2 files changed, 12 insertions(+), 1 deletion(-)

    --
    2.1.4

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