Re: [PATCH] m68k: coldfire: Prevent spurious interrupts when masking IMR

[Jean-Michel Hautbois]

Hi Geert,

On 04/02/2025 20:27, Geert Uytterhoeven wrote:
> Hi Jean-Michel,
>
> On Tue, 4 Feb 2025 at 19:38, Jean-Michel Hautbois
> <jeanmichel.hautbois@xxxxxxxxxx> wrote:
> > The ColdFire interrupt controller can generate spurious interrupts if an
> > interrupt source is masked in the IMR while the CPU interrupt priority
> > mask (SR[I]) is set lower than the interrupt level.
> >
> > The reference manual states:
> >
> > To avoid this situation for interrupts sources with levels 1-6, first
> > write a higher level interrupt mask to the status register, before
> > setting the mask in the IMR or the module’s interrupt mask register.
> > After the mask is set, return the interrupt mask in the status register
> > to its previous value.
> >
> > It can be tested like this:
> > - Prepare a iperf3 server on the coldfire target (iperf3 -s -D)
> > - Start a high priority cyclictest:
> >      cyclictest --secaligned -m -p 99 -i 2500 -q
> > - Start iperf3 -c $COLDFIRE_IP -t 0
> >
> > After a few seconds the dmesg may display:
> > [   84.784301] irq 24, desc: dbc502da, depth: 1, count: 0, unhandled: 0
> > [   84.784455] ->handle_irq():  0ba0aca3, handle_bad_irq+0x0/0x1e0
> > [   84.784610] ->irq_data.chip(): c6779d4f, 0x41652544
> > [   84.784719] ->action(): 00000000
> > [   84.784770] unexpected IRQ trap at vector 18
> >
> > With this patch, I never saw it in a few hours testing.
> >
> > Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@xxxxxxxxxx>
>
> Thanks for your patch!
>
> > --- a/arch/m68k/coldfire/intc-simr.c
> > +++ b/arch/m68k/coldfire/intc-simr.c
> > @@ -58,6 +58,14 @@ static inline unsigned int irq2ebit(unsigned int irq)
> >
> >   #endif
> >
> > +static inline void intc_irq_setlevel(unsigned long level)
> > +{
> > +       asm volatile ("move.w %0,%%sr"
> > +                     : /* no outputs */
> > +                     : "d" (0x2000 | ((level) << 8))
> > +                     : "memory");
> > +}
> > +
> >   /*
> >    *     There maybe one, two or three interrupt control units, each has 64
> >    *     interrupts. If there is no second or third unit then MCFINTC1_* or
> > @@ -67,13 +75,17 @@ static inline unsigned int irq2ebit(unsigned int irq)
> >   static void intc_irq_mask(struct irq_data *d)
> >   {
> >          unsigned int irq = d->irq - MCFINT_VECBASE;
> > +       unsigned long flags = arch_local_save_flags();
> >
> > +       intc_irq_setlevel(7);
>
> Can't all of the above just be replaced by
>
>      unsigned long flags = arch_local_irq_save();

I will check it again, but it seems a bit different. Now I get:
[   97.919407] hrtimer: interrupt took 203520 ns
[  161.757921] irq 24, desc: 24ef8971, depth: 1, count: 0, unhandled: 0
[  161.758074] ->handle_irq():  60d6a158, handle_bad_irq+0x0/0x1e0
[  161.758241] ->irq_data.chip(): 93aaf7a5, 0x4164e544
[  161.758359] ->action(): 00000000
[  161.758415] unexpected IRQ trap at vector 18

So, maybe isn't it exactly the same after all ?

JM

> >          if (MCFINTC2_SIMR && (irq > 127))
> >                  __raw_writeb(irq - 128, MCFINTC2_SIMR);
> >          else if (MCFINTC1_SIMR && (irq > 63))
> >                  __raw_writeb(irq - 64, MCFINTC1_SIMR);
> >          else
> >                  __raw_writeb(irq, MCFINTC0_SIMR);
> > +
> > +       arch_local_irq_restore(flags);
> >   }
> >
> >   static void intc_irq_unmask(struct irq_data *d)
>
> Gr{oetje,eeting}s,
>
>                          Geert