linux-kernel - Re: [PATCH v2 5/6] PCI: brcmstb: Add panic/die handler to RC driver

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Date:   Tue, 1 Dec 2020 15:12:54 -0500
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Mark Brown <broonie@...nel.org>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] PCI: brcmstb: Add panic/die handler to RC driver

On Tue, Dec 1, 2020 at 1:05 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Mon, Nov 30, 2020 at 04:11:42PM -0500, Jim Quinlan wrote:
> > Whereas most PCIe HW returns 0xffffffff on illegal accesses and the like,
> > by default Broadcom's STB PCIe controller effects an abort.  This simple
> > handler determines if the PCIe controller was the cause of the abort and if
> > so, prints out diagnostic info.
>
> What happens during enumeration?  pci_bus_generic_read_dev_vendor_id()
> assumes a read of Vendor ID returns 0xffffffff if the device doesn't
> exist.
>
> I assume this case doesn't cause the abort you're referring to here,
> or nothing would work.  I think this enumeration case results in PCIe
> Unsupported Request errors (PCIe r5.0, sec 2.3.2 implementation note).
Hi Bjorn,

Yes, our controller makes a special case  to allow for config-space
accesses to the dev_id and vendor_id registers. even if the device is
missing.  That being said, it will abort on any access if the link is
down.

However, the 7216-type SOCs bring PCIe error-reporting HW but also
have a mode where 0xffffffff  is returned on improper accesses, just
like many other controllers.  We are debating whether we should turn
this on by default.

Regards,
Jim Quinlan
Broadcom STB
>
> Bjorn

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