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    SubjectRe: [PATCHv2 2/2] ARM: debug: Move DEBUG_ICEDCC into the DEBUG_LL choice
    Hi Russell,

    On Thu, Sep 29, 2011 at 10:46:02AM +0100, Russell King - ARM Linux wrote:
    > On Thu, Sep 29, 2011 at 10:42:43AM +0100, Will Deacon wrote:
    > > Bah, just took this for a spin on my Realview-PBX (Cortex-A9) platform and
    > > the board won't boot unless I have a hardware debugger enabled that can
    > > service the comms channel. This contradicts the Kconfig text which says:
    > >
    > > It does include a timeout to ensure that the system does not
    > > totally freeze when there is nothing connected to read.
    > >
    > > so we certainly need to fix something!
    > One of the problems you'll encounter is that there's places where we
    > don't have any timer infrastructure (eg, decompressor) and software
    > timing loops won't work (they'll be too slow for the lower-end CPUs
    > and too fast for the upper-end CPUs.)

    Agreed, software timing loops are the only option and it's impossible to get
    them right everywhere. I think the Kconfig help text should be updated so
    that the timeout paragraph is removed.

    > The best fix is probably to leave that as-is, but introduce a 'default'
    > output entry instead - so platforms which don't have any listed will
    > get that instead of the ICEDDC stuff.

    Ok. Rather than 'default' (which people will probably select in preference
    to choosing the correct UART) how about something like below? I can split
    this into two patches if you prefer.



    diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
    index 32b1be4..bfdf86b 100644
    --- a/arch/arm/Kconfig.debug
    +++ b/arch/arm/Kconfig.debug
    @@ -81,6 +81,14 @@ choice
    prompt "Kernel low-level debugging port"
    depends on DEBUG_LL

    + config DEBUG_LL_UART_NONE
    + bool "No low-level debugging UART"
    + help
    + Say Y here if your platform doesn't provide a UART option
    + below. This relies on your platform choosing the right UART
    + definition internally in order for low-level debugging to
    + work.
    config DEBUG_ICEDCC
    bool "Kernel low-level debugging via EmbeddedICE DCC channel"
    @@ -89,8 +97,8 @@ choice
    co-processor 14. This is known to work on the ARM9 style ICE
    channel and on the XScale with the PEEDI.

    - It does include a timeout to ensure that the system does not
    - totally freeze when there is nothing connected to read.
    + Note that this may cause the system to hang during boot if
    + there is nothing to read from the DCC.

    bool "Kernel low-level debugging messages via footbridge 8250 at PCI COM1"

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