Re: [PATCH v4 2/8] irqchip: Add Realtek RTD1295 mux driver

[Marc Zyngier]

On 2019-11-19 23:33, Andreas FÃrber wrote:
> Am 19.11.19 um 23:29 schrieb Marc Zyngier:
> > On Tue, 19 Nov 2019 21:56:48 +0100
> > Andreas FÃrber <afaerber@xxxxxxx> wrote:
> > > Am 19.11.19 um 13:01 schrieb Marc Zyngier:
> > > > On 2019-11-19 02:19, Andreas FÃrber wrote:
> > > > > +static void rtd1195_mux_enable_irq(struct irq_data *data)
> > > > > +{
> > > > > +ÂÂÂ struct rtd1195_irq_mux_data *mux_data =
> > > > > irq_data_get_irq_chip_data(data);
> > > > > +ÂÂÂ unsigned long flags;
> > > > > +ÂÂÂ u32 mask;
> > > > > +
> > > > > +ÂÂÂ mask = mux_data->info->isr_to_int_en_mask[data->hwirq];
> > > > > +ÂÂÂ if (!mask)
> > > > > +ÂÂÂÂÂÂÂ return;
> > > >
> > > > How can this happen? You've mapped the interrupt, so it exists.
> > > > I can't see how you can decide to fail such enable.
> > >
> > > The [UMSK_]ISR bits and the SCPU_INT_EN bits are not (all) the 
> > > same.
> > >
> > > My ..._isr_to_scpu_int_en[] arrays have 32 entries for O(1) lookup, 
> > > but
> > > are sparsely populated. So there are circumstances such as WDOG_NMI 
> > > as
> > > well as reserved bits that we cannot enable.
> >
> > But the you should have failed the map. The moment you allow the
> > mapping to occur, you have accepted the contract that this interrupt 
> > is
> > usable.
> >
> > > This check should be
> > > identical to v3; the equivalent mask check inside the interrupt 
> > > handler
> > > was extended with "mask &&" to do the same in this v4.
> >
> > Spurious interrupts are a different matter. What I'm objecting to 
> > here
> > is a simple question of logic, whether or not you are allowed to 
> > fail
> > enabling an interrupt that you've otherwise allowed to be populated.
>
> Then what are you suggesting instead? I don't see how my array map
> lookup could fail other than returning a zero value, given its static
> initialization. Check for a zero mask in 
> rtd1195_mux_irq_domain_map()?
> Then we wouldn't be able to use the mentioned WDOG_NMI. Add another
> per-mux info field for which interrupts are valid to map?

I'm suggesting that you fail the map if you're unable to allow the
interrupt to be enabled.

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