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SubjectRe: [RFC Patch v1 2/4] irqchip/gic-v3: Add support to handle SGI as pseudo NMI
On 2020-04-25 11:29, Marc Zyngier wrote:
> On Fri, 24 Apr 2020 16:39:12 +0530
> Sumit Garg <sumit.garg@linaro.org> wrote:
>
> Hi Sumit,
>
>> With pseudo NMIs enabled, interrupt controller can be configured to
>> deliver SGI as a pseudo NMI. So add corresponding handling for SGIs.
>>
>> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
>> ---
>> drivers/irqchip/irq-gic-v3.c | 22 +++++++++++++++++-----
>> 1 file changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3.c
>> b/drivers/irqchip/irq-gic-v3.c
>> index d7006ef..be361bf 100644
>> --- a/drivers/irqchip/irq-gic-v3.c
>> +++ b/drivers/irqchip/irq-gic-v3.c
>> @@ -609,17 +609,29 @@ static inline void gic_handle_nmi(u32 irqnr,
>> struct pt_regs *regs)
>> if (irqs_enabled)
>> nmi_enter();
>>
>> - if (static_branch_likely(&supports_deactivate_key))
>> - gic_write_eoir(irqnr);
>> /*
>> * Leave the PSR.I bit set to prevent other NMIs to be
>> * received while handling this one.
>> * PSR.I will be restored when we ERET to the
>> * interrupted context.
>> */
>> - err = handle_domain_nmi(gic_data.domain, irqnr, regs);
>> - if (err)
>> - gic_deactivate_unhandled(irqnr);
>> + if (likely(irqnr > 15)) {
>> + if (static_branch_likely(&supports_deactivate_key))
>> + gic_write_eoir(irqnr);
>> +
>> + err = handle_domain_nmi(gic_data.domain, irqnr, regs);
>> + if (err)
>> + gic_deactivate_unhandled(irqnr);
>> + } else {
>> + gic_write_eoir(irqnr);
>> + if (static_branch_likely(&supports_deactivate_key))
>> + gic_write_dir(irqnr);
>> +#ifdef CONFIG_SMP
>> + handle_IPI(irqnr, regs);
>> +#else
>> + WARN_ONCE(true, "Unexpected SGI received!\n");
>> +#endif
>> + }
>>
>> if (irqs_enabled)
>> nmi_exit();
>
> If there is one thing I would like to avoid, it is to add more ugly
> hacks to the way we handle SGIs. There is very little reason why SGIs
> should be handled differently from all other interrupts. They have the
> same properties, and it is only because of the 32bit legacy that we
> deal
> with them in such a cumbersome way. Nothing that we cannot fix though.
>
> What I would really like to see is first a conversion of the SGIs to
> normal, full fat interrupts. These interrupts can then be configured as
> NMI using the normal API.
>
> I think Julien had something along these lines (or was that limited to
> the PMU?). Otherwise, I'll happily help you with that.

OK, to give you an idea of what I am after, here's a small series[1]
that
can be used as a base (it has been booted exactly *once* on a model, and
is thus absolutely perfect ;-).

There is still a bit of work to be able to actually request a SGI (they
are hard-wired as chained interrupts so far, as this otherwise changes
the output of /proc/interrupts, among other things), but you will
hopefully see what I'm aiming for.

Thanks,

M.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/gic-sgi
--
Jazz is not dead. It just smells funny...

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