Re: [PATCH] irqchip: mips-cpu: Remove eoi operation

[Marc Zyngier]

On 2020-01-15 14:23, Jiaxun Yang wrote:
> ä 2020å1æ15æ GMT+08:00 äå9:40:31, Marc Zyngier <maz@xxxxxxxxxx> åå:
> > On 2020-01-14 23:30, Paul Burton wrote:
> > > Hi Jiaxun,
> > >
> > > On Mon, Jan 13, 2020 at 06:12:51PM +0800, Jiaxun Yang wrote:
> > > > The eoi opreation in mips_cpu_irq_controller caused
> > chained_irq_enter
> > > > falsely consider CPU IP interrupt as a FastEOI type IRQ. So the
> > > > interrupt
> > > > won't be masked during in handler. Which might lead to spurious
> > > > interrupt.
> > > >
> > > > Thus we simply remove eoi operation for mips_cpu_irq_controller,
> > > >
> > > > Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
> > > > ---
> > > >  drivers/irqchip/irq-mips-cpu.c | 1 -
> > > >  1 file changed, 1 deletion(-)
> > > >
> > > > diff --git a/drivers/irqchip/irq-mips-cpu.c
> > > > b/drivers/irqchip/irq-mips-cpu.c
> > > > index 95d4fd8f7a96..0ad7f1f9a58b 100644
> > > > --- a/drivers/irqchip/irq-mips-cpu.c
> > > > +++ b/drivers/irqchip/irq-mips-cpu.c
> > > > @@ -55,7 +55,6 @@ static struct irq_chip mips_cpu_irq_controller = {
> > > >  	.irq_mask	= mask_mips_irq,
> > > >  	.irq_mask_ack	= mask_mips_irq,
> > > >  	.irq_unmask	= unmask_mips_irq,
> > > > -	.irq_eoi	= unmask_mips_irq,
> > > >  	.irq_disable	= mask_mips_irq,
> > > >  	.irq_enable	= unmask_mips_irq,
> > > >  };
> > >
> > > This one scares me; something doesn't seem right. The irq_eoi (nÃe
> > eoi)
> > > callback was first added way back in commit 1417836e81c0 ("[MIPS] use
> > > generic_handle_irq, handle_level_irq, handle_percpu_irq"). The commit
> > > message there states that the motivation was to allow use of
> > > handle_percpu_irq(), and indeed handle_percpu_irq() does:
> > >
> > >     irq_ack() (ie. mask)
> > >     invoke the handler(s)
> > >     irq_eoi() (ie. unmask)
> > >
> > > By removing the irq_eoi callback I don't see how we'd ever unmask the
> > > interrupt again..?
> >
> > To be completely blunt, the fact that unmask and eoi are implemented
> > the
> > same way is a clear sign that this is a bit broken.
> >
> > irq_eoi is used if the irqchip tracks the IRQ life-cycle in HW, and
> > it's
> > not obvious that this is the case. The fact that ack is also mapped to
> > mask
>
> It's just a kind of hack to workaround the fact that our current
> percpu irq handler assumed
> all percpu irqs are edge triggered or fasteoi type.
>
> However MIPS processor implemented it in level triggered way.
>
> My solution would be add a check. If neither ack nor eoi exist for the 
> chip,
> than we assume it's level triggered and process precpu irq in 
> mask/unmask way.
>
> Could it be a possible option?

Post the patch, and we'll discuss it.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...