linux-kernel - Re: [PATCH] x86/ioapic: add IO-APIC irq

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Date:   Wed, 18 Jan 2017 16:26:14 +0200
From:   "Ruslan Ruslichenko -X (rruslich - GLOBALLOGIC INC at Cisco)" 
        <rruslich@...co.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        xe-linux-external@...co.com
Subject: Re: [PATCH] x86/ioapic: add IO-APIC irq_chip retrigger hook

On 01/18/2017 12:46 PM, Thomas Gleixner wrote:
> On Tue, 17 Jan 2017, Ruslan Ruslichenko wrote:
>
>> After commit d32932d02e18  ("x86/irq: Convert IOAPIC to use hierarchical
>> irqdomain interfaces") IO-APIC is switched to hierarchical irqdomain
>> implementation. Also this patch removed irq_retrigger hook for IO-APIC
>> chip which seem to be wrong. Without this hook some edge-triggered irq's
>> might be lost, since kernel uses it to retrigger edge irq's triggered
>> while they are being handled or disabled by driver
> Restoring the callbacks is the right thing to do, but there is no problem
> because if the retrigger callback is empty then pending edge interrupts are
> resent by software. It's just less efficient, but not a issue.

Software resend will only work if CONFIG_HARDIRQS_SW_RESEND is enabled,
which is not selected for x86 architectures.

So it's good that patch now picked up.
> Thanks,
>
> 	tglx