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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 28 Apr 2021 14:21:27 +0200
Message-ID: <CAJZ5v0jEbjRSGPdfwvegawin5_N=m-UoP+Wa99EQ-QmkusiBCg@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] pci: Support "removable" attribute for PCI devices
To:     Oliver Neukum <oneukum@suse.com>
Cc:     David Laight <David.Laight@aculab.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rajat Jain <rajatja@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@vger.kernel.org>, Bjorn Helgaas <helgaas@kernel.org>,
        Rajat Jain <rajatxjain@gmail.com>,
        Jesse Barnes <jsbarnes@google.com>,
        Dmitry Torokhov <dtor@google.com>
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On Wed, Apr 28, 2021 at 8:57 AM Oliver Neukum <oneukum@suse.com> wrote:
>
> Am Dienstag, den 27.04.2021, 12:59 +0000 schrieb David Laight:
> > From: Oliver Neukum
> > > Sent: 27 April 2021 13:00
>
> > > that is true for those options, but not for the style
> > > of PCI hotplug which requires you to push a button and wait
> > > for the blinking light.
> >
> > True, I remember some of those PCI hotplug chassis from 25 years ago.
> > ISTR we did get the removal events working (SVR4/Unixware) but I
> > don't remember the relevant chassis ever being sold.
> > In spite of the marketing hype I suspect it was only ever possible
> > to remove a completely working board and replace it with an
> > exactly equivalent one.
> >
> > In any case those chassis are not 'surprise removal'.
> >
> > More modern drivers are less likely to crash (and burn?) when
> > a PCI read returns ~0u.
> > But I suspect an awful lot really don't handle surprise removal
> > very well at all.
>
> So you are saying that these systems are so rare that it should be
> handled  as special cases if at all?

In principle, in the wake of Thunderbolt every PCI driver handling
PCIe devices needs to be able to deal with a device that's gone away
without notice, because in principle any PCIe device can be included
into a Thunderbolt docking station which may go away as a whole
without notice.