Re: [PATCH 3/6] irqchip: RISC-V Local Interrupt Controller Driver

[Atish Patra]

On 7/25/18 4:37 AM, Marc Zyngier wrote:
> On 25/07/18 12:24, Christoph Hellwig wrote:
> > On Wed, Jul 25, 2018 at 12:18:39PM +0100, Marc Zyngier wrote:
> > > This feels odd. It means that you cannot have the following sequence:
> > >
> > > 	local_irq_disable();
> > > 	enable_irq(x); // where x is owned by a remote hart
> > >
> > > as smp_call_function_single() requires interrupts to be enabled.
> > >
> > > More fundamentally, why are you trying to make these interrupts look
> > > global while they aren't? arm/arm64 have similar restrictions with GICv2
> > > and earlier, and treats these interrupts as per-cpu.
> > >
> > > Given that the drivers that deal with drivers connected to the per-hart
> > > irqchip are themselves likely to be aware of the per-cpu aspect, it
> > > would make sense to align things (we've been through that same
> > > discussion about the clocksource driver a few weeks back).
> >
> > Right now the only direct consumers are said clocksource, the PLIC
> > driver later in this series and the RISC-V arch IPI code.  None of them
> > is going to do a manual enable_irq, so I guess the remote case of the
> > code is simply dead code.  I'll take a look at converting them to
> > per-cpu.  I guess the GICv2 driver is the best template?
>
> I think you can do a much better job than the GICv2 driver ;-). You have
> the chance of a clean slate, and no legacy (or ACPI) junk to deal with!
>
> I think this is just a matter of moving the HLIC declaration in DT to be
> outside of the cpu nodes (you just have a single HLIC node that is valid
> for all the CPUs in the system), and making the interrupts percpu_devid
> in your mapping function (see gic_irq_domain_map for reference).

If I am not wrong, we need to change the interrupt-extended property in 
PLIC DT entry as well. Currently, there are 5 entries corresponding to 
individual HLIC. I was also planning to start working on converting HLIC 
to per-cpu but it got delayed because of travel.

Christoph: I am not sure if you have access to HighFive Unleashed board. 
If not I would be happy to test it on the board whenever your patches 
are ready.

Regards,
Atish
> Thanks,
>
> 	M.