linux-kernel - Re: [PATCH 10/10] clocksource/drivers/hyper-v: Move handling of STIMER0 interrupts

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Date:   Mon, 1 Feb 2021 19:53:27 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     sthemmin@...rosoft.com, kys@...rosoft.com, wei.liu@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        daniel.lezcano@...aro.org, arnd@...db.de,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 10/10] clocksource/drivers/hyper-v: Move handling of
 STIMER0 interrupts

On Wed, Jan 27, 2021 at 12:23:45PM -0800, Michael Kelley wrote:
[...]
> +static int hv_setup_stimer0_irq(void)
> +{
> +	int ret;
> +
> +	ret = acpi_register_gsi(NULL, HYPERV_STIMER0_VECTOR,
> +			ACPI_EDGE_SENSITIVE, ACPI_ACTIVE_HIGH);

When IO-APIC is enabled on x86, acpi_register_gsi calls
mp_map_gsi_to_irq. That function then calls mp_find_ioapic. Is
HYPERV_STIMER0_VECTOR, when used as a GSI, associated with an IO-APIC?
If not, wouldn't mp_find_ioapic return an error causing
acpi_register_gsi to fail?

Ah, it appears that this function is not called on x86. I haven't
checked how ARM handles GSI, but presumably this works for you.  It
would be good if a comment can be added to clarify things.

Wei.