Messages in this thread Patch in this message |  | | Date | Thu, 29 Sep 2011 11:39:39 +0100 | | From | Will Deacon <> | | Subject | Re: [PATCHv2 2/2] ARM: debug: Move DEBUG_ICEDCC into the DEBUG_LL choice |
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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.
Will
----8<----
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" help @@ -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. config DEBUG_FOOTBRIDGE_COM1 bool "Kernel low-level debugging messages via footbridge 8250 at PCI COM1"
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