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Date:   Sat, 12 Nov 2022 21:07:15 +0100
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Subject: Re: [PATCH v2] acpi,pci: handle duplicate IRQ routing entries
 returned from _PRT
To:     Bjorn Helgaas <helgaas@kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-acpi@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Len Brown <lenb@kernel.org>, Borislav Petkov <bp@suse.de>,
        Jean Delvare <jdelvare@suse.com>, linux-i2c@vger.kernel.org
References: <20221112002023.GA764787@bhelgaas>
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From:   =?UTF-8?Q?Mateusz_Jo=c5=84czyk?= <mat.jonczyk@o2.pl>
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W dniu 12.11.2022 o 01:20, Bjorn Helgaas pisze:
> [+cc Jean, linux-i2c]
>
> On Sat, Sep 17, 2022 at 11:09:44AM +0200, Mateusz Jończyk wrote:
>> On some platforms, the ACPI _PRT function returns duplicate interrupt
>> routing entries. Linux uses the first matching entry, but sometimes the
>> second matching entry contains the correct interrupt vector.
> Rafael, Jean, what do you think about this?  It seems like kind of a
> lot of infrastructure to deal with this oddness, but I'm not really
> opposed to it.
>
> This is in i2c-i801.c, which seems to have some support for polling;
> maybe it could make smart enough to complain and automatically switch
> to polling if a timeout occurs.
>
> Or maybe we scan the entire _PRT and let the match win (instead of the
> first as we do today).
>
> Or ...?
>
> Google finds a lot of hits for "i801_smbus" "timeout waiting for
> interrupt", but I can't tell whether they're a similar _PRT issue or
> something else.
>
>> This happens on a Dell Latitude E6500 laptop with the i2c-i801 Intel
>> SMBus controller. This controller was nonfunctional unless its interrupt
>> usage was disabled (using the "disable_features=0x10" module parameter).

Hello,

I have prepared a lean patch that only prints a warning when there are
two matching entries in the table returned from _PRT (I will send it in the
next e-mail). Perhaps it could be merged and then after a release or two
it will be known how widespread this problem is.

Greetings,

Mateusz