linux-kernel - Re: [PATCH 3/3] PCI: pciehp: Add dmi table for in-band presence disabled

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Date:   Tue, 1 Oct 2019 16:36:22 -0500
From:   "Alex G." <mr.nuke.me@...il.com>
To:     Stuart Hayes <stuart.w.hayes@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, lukas@...ner.de
Subject: Re: [PATCH 3/3] PCI: pciehp: Add dmi table for in-band presence
 disabled



On 10/1/19 4:14 PM, Stuart Hayes wrote:
> Some systems have in-band presence detection disabled for hot-plug PCI slots,
> but do not report this in the slot capabilities 2 (SLTCAP2) register.  On
> these systems, presence detect can become active well after the link is
> reported to be active, which can cause the slots to be disabled after a
> device is connected.
> 
> Add a dmi table to flag these systems as having in-band presence disabled.
> 
> Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
> ---
>   drivers/pci/hotplug/pciehp_hpc.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 1282641c6458..1dd01e752587 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -14,6 +14,7 @@
>   
>   #define dev_fmt(fmt) "pciehp: " fmt
>   
> +#include <linux/dmi.h>
>   #include <linux/kernel.h>
>   #include <linux/types.h>
>   #include <linux/jiffies.h>
> @@ -26,6 +27,16 @@
>   #include "../pci.h"
>   #include "pciehp.h"
>   
> +static const struct dmi_system_id inband_presence_disabled_dmi_table[] = {
> +	{
> +		.ident = "Dell System",
> +		.matches = {
> +			DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc"),
> +		},
> +	},
> +	{}
> +};
> +

I'm not sure that all Dell systems that were ever made or will be made 
have in-band presence disabled on all their hotplug slots.

This was a problem with the NVMe hot-swap bays on 14G servers. I can't 
guarantee that any other slot or machine will need this workaround. The 
best way I found to implement this is to check for the PCI-ID of the 
switches behind the port.

Alex