Re: [Xen-devel] [RFC PATCH 17/49] ARM: timer: Handle level triggered IRQs correctly

[Julien Grall <julien.grall@xxxxxxx>]

On 12/02/18 18:23, Andre Przywara wrote:
> Hi,
Hi Andre,

> On 12/02/18 15:19, Julien Grall wrote:
> > Hi Andre,
> >
> > On 09/02/18 14:39, Andre Przywara wrote:
> > > The ARM Generic Timer uses a level-sensitive interrupt semantic. We
> > > easily catch when the line goes high, as this triggers the hardware IRQ.
> > > However we have to sync the state of the interrupt condition at certain
> > > points to catch when the line goes low and we can remove the vtimer vIRQ
> > > from the vGIC (and the LR).
> > > The VGIC in Xen so far only implemented edge triggered vIRQs, really, so
> > > we need to add new functionality to re-sample the interrupt state.
> > You might want to make a summary of the discussion we had with Marc Z.
> > today here. This would help the other to understand why sample the
> > interrupt state is necessary :).
> Yes, I just saw that I somehow missed copying the elaborate comment from
> Christoffer. Fixed now, indeed without this background it's next to
> impossible to understand this ;-)
>
> > Also do we need to do that for the emulated physical timer?
> Mmh, good question. I believe this whole timer story needs a good think
> again.
>
> > > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxx>
> > > ---
> > >    xen/arch/arm/time.c     | 34 ++++++++++++++++++++++++++++++++++
> > >    xen/arch/arm/traps.c    |  1 +
> > >    xen/include/xen/timer.h |  2 ++
> > >    3 files changed, 37 insertions(+)
> > >
> > > diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
> > > index c11fcfeadd..98ebb4305d 100644
> > > --- a/xen/arch/arm/time.c
> > > +++ b/xen/arch/arm/time.c
> > > @@ -263,6 +263,40 @@ static void vtimer_interrupt(int irq, void
> > > *dev_id, struct cpu_user_regs *regs)
> > >        vgic_inject_irq(current->domain, current,
> > > current->arch.virt_timer.irq, true);
> > >    }
> > >    +/**
> > One * is enough.
> That's kernel-doc comment style:
> https://www.kernel.org/doc/html/v4.9/kernel-documentation.html#writing-kernel-doc-comments
>
> That allows tools to scan the tree and extract function documentation in
> an automated way. A bit like markdown: still perfectly readable by
> humans, but parse-able by scripts as well.
>
> I was hoping that it wouldn't hurt to have this in Xen as well, as I
> copied this already in other parts of this code.
I was blindly following the CODING_STYLE requirements :). But let's keep 
/** if it helps script.
Cheers,

--
Julien Grall

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