Re: [PATCH RESEND 16/17] MIPS: make oprofile use cp0_perfcount_irq if it is set

[Ralf Baechle <ralf@linux-mips.org>]

On Thu, Jan 12, 2012 at 06:38:22PM +0300, Sergei Shtylyov wrote:

> >@@ -374,6 +379,10 @@ static int __init mipsxx_init(void)
> >     save_perf_irq = perf_irq;
> >     perf_irq = mipsxx_perfcount_handler;
> >
> >+    if (cp0_perfcount_irq>= 0)
> 
>    BTW, I just noticed. IRQ0 is not a valid IRQ in Linux,
> request_irq() should fail when passed 0, so this and following check
> should be '> 0'.

In a normal configuration that is in a discrete processor or in a MIPS
core where the performance IRQ is just routed back into the core the
lowest sensible value for cp0_perfcount_irq is 2, so there is no
immediate problem there.

IRQ 0 is ok for static use; dynamic use is problematic.  This case is
even more problematic because the interrupt might be shared with the
timer and the timer interrupt is allocated statically (see cevt-r4k.c)
but the performance counter interrupt later allocated dynamically with
IRQF_SHARED.

  Ralf