linux-kernel - Re: [PATCH] x86: ioapic needs check attr when programmed more than once

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Date:	Fri, 23 Aug 2013 16:04:32 +0800
From:	Liu ping fan <kernelfans@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Kevin Hao <haokexin@...il.com>
Subject: Re: [PATCH] x86: ioapic needs check attr when programmed more than once

On Fri, Aug 23, 2013 at 3:30 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Liu Ping Fan <kernelfans@...il.com> wrote:
>
>> When programming ioapic pinX more than once, current code
>> does not check whether the later attr (trigger&polarity) is the
>> same as the former or not. This causes a broken semantic.
>>
>> Fix it by reporting -EBUSY, when attr is different.
>
> Was this observed in real life somehow, and if yes, what is
> the before/after behavior?
>
Using qemu q35 machine, I found the ioapic's ioredtbl[] will never has
low-active, even the hpet driver registered it. After tracing, I found
it shared a high-level active IRQ line with other device. So in fact,
the acpi_register_gsi(, ACPI_ACTIVE_LOW) in hpet driver fail, but it
did not detect it.
The effect in qemu: when hpet-dev assert low-level, the kernel can not respond.


Thanks,
Pingfan
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