On Monday 29 June 2009 17:19:31 Russell King - ARM Linux wrote: > On Mon, Jun 29, 2009 at 04:31:18PM +0200, Jean Pihet wrote: > > I am trying to get the latest IRQ registers from a timer or a work queue > > but I am running into problems: > > - get_irq_regs() returns NULL in some cases, > > It will always return NULL outside of IRQ context - and only returns valid > pointers when used inside IRQ context. Ok got it. > It's one of these things that nests itself - when you have several IRQs > being processed on one CPU, there are several register contexts saved, > and get_irq_regs() returns the most recent one. > > > The use case is that the performance unit (PMNC) of the Cortex A8 has > > some serious bug, in short the performance counters overflow IRQ is to be > > avoided. > > I don't follow. None of the PMNC support code in the mainline kernel > uses get_irq_regs() outside of IRQ context. That is correct. The Cortex A8 needs some special treatment. The errata says that if the counters are overflowing at the same time as a coprocessor access is performed, the perf unit gets reset and/or locks up. In short the counters overflow is to be avoided and so the PMNC IRQ. > > Some questions: > > - is there a way to get the last 'real' IRQ registers from a timer or > > work queue handler? > > No. Outside of IRQ events, the saved IRQ context does not exist. Ok. I wonder how to implement it correctly from here. The ultimate goal is to feed the registers to oprofile for statistics gathering (mostly the PC). I do not see much benefit from oprofile without the PC statistics. Thanks, Jean -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
