linux-kernel - Re: [PATCH v4 2/2] PCI: Enable NO_BUS

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Date:   Wed, 5 May 2021 13:56:47 +1000
From:   "Oliver O'Halloran" <oohall@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Shanker R Donthineni <sdonthineni@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sinan Kaya <okaya@...nel.org>,
        Vikram Sethi <vsethi@...dia.com>,
        Amey Narkhede <ameynarkhede03@...il.com>
Subject: Re: [PATCH v4 2/2] PCI: Enable NO_BUS_RESET quirk for Nvidia GPUs

On Wed, May 5, 2021 at 12:50 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Mon, May 03, 2021 at 09:07:11PM -0500, Shanker R Donthineni wrote:
> > On 5/3/21 5:42 PM, Bjorn Helgaas wrote:
> > > Obviously _RST only works for built-in devices, since there's no AML
> > > for plug-in devices, right?  So if there's a plug-in card with this
> > > GPU, neither SBR nor _RST will work?
> > These are not plug-in PCIe GPU cards, will exist on upcoming server
> > baseboards. ACPI-reset should wok for plug-in devices as well as long
> > as firmware has _RST method defined in ACPI-device associated with
> > the PCIe hot-plug slot.
>
> Maybe I'm missing something, but I don't see how _RST can work for
> plug-in devices.  _RST is part of the system firmware, and that
> firmware knows nothing about what will be plugged into the slot.  So
> if system firmware supplies _RST that knows how to reset the Nvidia
> GPU, it's not going to do the right thing if you plug in an NVMe
> device instead.
>
> Can you elaborate on how _RST would work for plug-in devices?

Power cycling the slot or just re-asserting #PERST probably. IBM has
been doing that on Power boxes since forever and it mostly works.
Mostly.