linux-kernel - Re: [PATCH 2/2] PCI: brcmstb: Add panic/die handler to driver

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Message-ID: <20250806181540.GA8692@bhelgaas>
Date: Wed, 6 Aug 2025 13:15:40 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jim Quinlan <james.quinlan@...adcom.com>
Cc: linux-pci@...r.kernel.org, Nicolas Saenz Julienne <nsaenz@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Cyril Brulebois <kibi@...ian.org>,
	bcm-kernel-feedback-list@...adcom.com, jim2101024@...il.com,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Rob Herring <robh@...nel.org>,
	"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 2/2] PCI: brcmstb: Add panic/die handler to driver

On Fri, Jun 13, 2025 at 06:08:43PM -0400, 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.  Some SoCs --
> 7216 and its descendants -- have new HW that identifies error details.

What's the long term plan for this?  This abort is a huge problem that
we're seeing across arm64 platforms.  Forcing a panic and reboot for
every uncorrectable error is pretty hard to deal with.

Is there a plan to someday recover from these aborts?  Or change the
hardware so it can at least be configured to return ~0 data after
logging the error in the hardware registers?

> This simple handler determines if the PCIe controller was the cause of the
> abort and if so, prints out diagnostic info.  Unfortunately, an abort still
> occurs.
> 
> Care is taken to read the error registers only when the PCIe bridge is
> active and the PCIe registers are acceptable.  Otherwise, a "die" event
> caused by something other than the PCIe could cause an abort if the PCIe
> "die" handler tried to access registers when the bridge is off.

Checking whether the bridge is active is a "mostly-works" situation
since it's always racy.

> Example error output:
>   brcm-pcie 8b20000.pcie: Error: Mem Acc: 32bit, Read, @0x38000000
>   brcm-pcie 8b20000.pcie:  Type: TO=0 Abt=0 UnspReq=1 AccDsble=0 BadAddr=0