linux-kernel - Re: [PATCH 0/2] i2c: i801: Force no IRQ for Dell Latitude E7450

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Message-ID: <20230604163144.1e6e5bef@endymion.delvare>
Date:   Sun, 4 Jun 2023 16:31:44 +0200
From:   Jean Delvare <jdelvare@...e.de>
To:     Marius Hoch <mail@...iushoch.de>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] i2c: i801: Force no IRQ for Dell Latitude E7450

Hi again Marius,

On Sun, 4 Jun 2023 16:01:32 +0200, Jean Delvare wrote:
> IRQ number 255 indeed looks suspicious, but I'm also not aware of this
> being a special value (nr_irqs is defined as an unsigned int, which
> suggest that large IRQ numbers, albeit unusual on desktop and laptop
> systems, are supported and frequently seen on large server systems), so
> the i2c-i801 driver has no reason to handle it in a particular way.

OK, I stand corrected. There's this interesting comment in
drivers/acpi/pci_irq.c:acpi_pci_irq_valid():

	/*
	 * On x86 irq line 0xff means "unknown" or "no connection"
	 * (PCI 3.0, Section 6.2.4, footnote on page 223).
	 */

So that's probably what you are seeing on your Dell laptop.

Unfortunately this function is static inline, so we can't call it from
the i2c-i801 driver. It's called by acpi_pci_irq_enable() but only if
(gsi < 0), which isn't the case on your system.

-- 
Jean Delvare
SUSE L3 Support