linux-kernel - Re: [PATCH 2/2] PCI: Unify pci_dev_is_disconnected() and pci_dev_is

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Message-ID: <20190904053523.7lmuoo5zempxtsdq@wunner.de>
Date:   Wed, 4 Sep 2019 07:35:23 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Kelsey Skunberg <skunberg.kelsey@...il.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        skhan@...uxfoundation.org, rafael.j.wysocki@...el.com,
        keith.busch@...el.com
Subject: Re: [PATCH 2/2] PCI: Unify pci_dev_is_disconnected() and
 pci_dev_is_inaccessible()

On Tue, Sep 03, 2019 at 10:36:35PM -0600, Kelsey Skunberg wrote:
> Change pci_dev_is_disconnected() call inside pci_dev_is_inaccessible() to:
> 
> 	pdev->error_state == pci_channel_io_perm_failure
> 
> Change remaining pci_dev_is_disconnected() calls to
> pci_dev_is_inaccessible() calls.

I don't think that's a good idea because it introduces a config space read
(for the vendor ID) in places where we don't want that.  E.g., after the
check of pdev->error_state, a regular config space read may take place and
if that returns all ones, we may already be able to determine that the
device is inaccessible, obviating the need for a vendor ID check.
Config space reads aren't for free.

Thanks,

Lukas