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

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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.


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