Messages in this thread | | | Date | Wed, 03 Sep 2014 10:02:18 +0100 | From | Daniel Thompson <> | Subject | Re: [PATCH v11 00/19] arm: KGDB NMI/FIQ support |
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On 03/09/14 00:02, Thomas Gleixner wrote: > On Tue, 2 Sep 2014, Daniel Thompson wrote: > >> This patchset makes it possible to use kgdb's NMI infrastructure on ARM >> platforms. >> >> The patches are seperated into three distinct groups: >> >> 1. arm specific changes; these provide multi-platform support for FIQ >> (including raising an IPI using FIQ to ensure effective SMP support) >> and extend ARM KGDB support to use the features provided. >> >> 2. irqchip changes; updates to the gic and vic drivers to provide >> support for routing certain interrupt sources to FIQ. >> >> 3. serial changes; driver support to allow the UART interrupt to be >> routed to FIQ. The already mainlined kgdb NMI infrastructure (mostly >> found in drivers/tty/serial/kgdb_nmi.c) will re-route the kgdb >> console UART's interrupt signal from IRQ to FIQ. Naturally the UART >> will no longer function normally and will instead be managed by kgdb >> using the polled I/O functions. Any character delivered to the UART >> causes the kgdb handler function to be called. > > To be honest, what you are doing is just ass backwards. > > The use case you are looking for is the most irrelevant of all. Just > because KGDB is on some managerial "must have items" checklist does > not make it useful.
The FIQ based interactive debugger use case is fairly common on Android, especially for Nexus devices (they have an out-of-tree debugger similar to kdb for this).
I think it finds favour there because during the development phases where the console is unplugged to allow developers to go walkabout live with a prototype phone. The interactive debugger is used for post-morteming when something breaks. At this stage of development are reluctant to expose/consume hardware resources (JTAG pins, RAM, FLASH) for JTAG or kexec/kdump post-mortems.
> The only relevant use cases of FIQs are the same as those of NMIs on > x86: > > - Watchdog to detect stuck cpus and issue stack traces
Russell put together a quick 'n dirty version of the NMI stack trace code based on a subset of my patchset. Based on his feedback, later revisions of my patchset are structured to simplify adding this code.
Daniel.
> - Performace monitoring > > KGDB falls into place once you solved the above. > > That said for the general approach, I'll have a look at the irq > related patches in a minute. > > Thanks, > > tglx
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