On Thursday 18 October 2007 03:25:42 Benjamin Herrenschmidt wrote:
> synchronize_irq needs at the very least a compiler barrier and a
> read barrier on SMP, but there are enough cases around where a
> write barrier is also needed and it's not a hot path so I prefer
> using a full smp_mb() here.
>
> It will degrade to a compiler barrier on !SMP.
>
> Signed-off-by: Benjamin Herrenschmidt <[email protected]>
> ---
>
> Index: linux-work/kernel/irq/manage.c
> ===================================================================
> --- linux-work.orig/kernel/irq/manage.c 2007-10-18 11:22:16.000000000 +1000
> +++ linux-work/kernel/irq/manage.c 2007-10-18 11:22:20.000000000 +1000
> @@ -33,6 +33,7 @@ void synchronize_irq(unsigned int irq)
> if (irq >= NR_IRQS)
> return;
>
> + smp_mb();
> while (desc->status & IRQ_INPROGRESS)
> cpu_relax();
> }
>
>
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>
Hi,
I have read this thread and I concluded few things:
1) It is impossible to know that the card won't send more interrupts:
Even if I do a read from the device, the IRQ can be pending in the bus/APIC
It is even possible (and likely) that the IRQ line will be shared, thus the
handler can be called by non-relevant device.
2) the synchronize_irq(); in .suspend is useless:
an IRQ can happen immediately after this synchronize_irq();
and interrupt even the .suspend()
(At least theoretically)
Thus I now understand that .suspend() should do:
saa_writel(SAA7134_IRQ1, 0);
saa_writel(SAA7134_IRQ2, 0);
saa_writel(SAA7134_MAIN_CTRL, 0);
dev->insuspend = 1;
smp_wmb();
/* at that point the _request to disable card's IRQs was issued, we don't know
that there will be no irqs anymore.
the smp_mb(); guaranties that the IRQ handler will bail out in that case. */
/* .......*/
pci_save_state(pci_dev);
pci_set_power_state(pci_dev, pci_choose_state(pci_dev, state));
return 0;
and the interrupt handler:
smp_rmb();
if (dev->insuspend)
goto out;
Am I right?
Best regards,
Maxim Levitsky
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