Re: get_irq_regs() from soft IRQ

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

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.

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.

> 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.

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