linux-kernel - Re: [PATCH v4 0/3] PCI: pciehp: Do not turn off slot if presence comes up after link

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Date:   Sat, 8 Feb 2020 21:22:53 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Stuart Hayes <stuart.w.hayes@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oliver Neukum <oneukum@...e.com>,
        Libor Pechacek <lpechacek@...e.cz>
Subject: Re: [PATCH v4 0/3] PCI: pciehp: Do not turn off slot if presence
 comes up after link

On Fri, Oct 25, 2019 at 03:00:44PM -0400, Stuart Hayes wrote:
> In older PCIe specs, PDS (presence detect) would come up when the
> "in-band" presence detect pin connected, and would be up before DLLLA
> (link active).
> 
> In PCIe 4.0 (as an ECN) and in PCIe 5.0, there is a new bit to show if
> in-band presence detection can be disabled for the slot, and another bit
> that disables it--and a recommendation that it should be disabled if it
> can be. In addition, certain OEMs disable in-band presence detection
> without implementing these bits.
> 
> This means it is possible to get a "card present" interrupt after the
> link is up and the driver is loaded.  This causes an erroneous removal
> of the device driver, followed by an immediate re-probing.
> 
> This patch set defines these new bits, uses them to disable in-band
> presence detection if it can be, waits for PDS to go up if in-band
> presence detection is disabled, and adds a DMI table that will let us
> know if we should assume in-band presence is disabled on a system.

FWIW, this series is

Reviewed-by: Lukas Wunner <lukas@...ner.de>

Looking at the patches again today, I only spotted a minor cosmetic issue:

In patch [1/3] I would have preferred readout of the PCI_EXP_SLTCAP2
register (hunk #3) to be inserted a little further up in pcie_init(),
perhaps before reading the PCI_EXP_LNKCAP register.  It just looks
a little out of place at the end of the function.  I would have
grouped it together with the other quirks and feature checks further
up in the function and I probably would have amended the ctrl_info()
to print the status of the inband_presence_disabled flag.

In patch [3/3] the DMI check would then likewise have to be moved up
in the function.

Maybe Bjorn can make this change when applying, and if not, it's not
a big deal.

Thanks,

Lukas