linux-kernel - boot interrupt quirk (also in 4.19.y) breaks serial ports (was: [PATCH v2 0/2] pci: Add boot interrupt quirk mechanism for Xeon chipsets)

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Message-ID: <b2da25c8-121a-b241-c028-68e49bab0081@tik.uni-stuttgart.de>
Date:   Wed, 16 Sep 2020 12:12:18 +0200
From:   "Stefan Bühler" 
        <stefan.buehler@....uni-stuttgart.de>
To:     sean.v.kelley@...ux.intel.com
Cc:     bhelgaas@...gle.com, bp@...en8.de, corbet@....net,
        kar.hin.ong@...com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        mingo@...hat.com, sassmann@...nic.de, tglx@...utronix.de,
        x86@...nel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: boot interrupt quirk (also in 4.19.y) breaks serial ports (was:
 [PATCH v2 0/2] pci: Add boot interrupt quirk mechanism for Xeon chipsets)

Hi,

this quirk breaks our serial ports PCIe card (i.e. we don't see any 
output from the connected devices; no idea whether anything we send 
reaches them):

05:00.0 PCI bridge: PLX Technology, Inc. PEX8112 x1 Lane PCI Express-to-PCI Bridge (rev aa)
06:00.0 Serial controller: Oxford Semiconductor Ltd OX16PCI954 (Quad 16950 UART) function 0 (Uart)
06:00.1 Bridge: Oxford Semiconductor Ltd OX16PCI954 (Quad 16950 UART) function 0 (Disabled)
06:01.0 Serial controller: Oxford Semiconductor Ltd OX16PCI954 (Quad 16950 UART) function 0 (Uart)
06:01.1 Bridge: Oxford Semiconductor Ltd OX16PCI954 (Quad 16950 UART) function 0 (Disabled)

The hardware is "MP8-PCIe-RS232-R2" (we also have the 16-port variant) 
from https://rs-232.de/sercom_e.htm#MP8PCIERS232

The CPU is an "Intel(R) Xeon(R) CPU D-1518 @ 2.20GHz".

Disabling the quirk for 0x6f28 (Xeon D-1500) on 4.19.145 gets the serial 
ports working again (patch attached for reference).

The box is running debian stable; we build ixgbe 5.6.1 through dkms 
(local package) due to issues with the SFP+ ports (usually our 
uplink...).

Known broken versions: 4.19.115-00065, 4.19.118, 4.19.145, 5.8.9
Known good versions: 4.19.115-00064

Basically if we see "kernel: pci 0000:00:05.0: disabled boot interrupts 
on device [8086:6f28]" in the kernel log it's broken.

Attached lspci, lscpu, lsmod and kernel log outputs while running 5.8.9.

Can we disable the quirk somehow via the kernel commandline?

Anything else I can do to help getting this fixed properly?

(We have the same card in other boxes with CPUs not affected by this 
quirk; they are working just fine.)

cheers,
Stefan

-- 
Stefan Bühler    Mail/xmpp: stefan.buehler@....uni-stuttgart.de
Netze und Kommunikationssysteme der Universität Stuttgart (NKS)
https://www.tik.uni-stuttgart.de/    Telefon: +49 711 685 60854

View attachment "lspci.txt" of type "text/plain" (9810 bytes)

View attachment "lscpu.txt" of type "text/plain" (1505 bytes)

View attachment "lsmod.txt" of type "text/plain" (4351 bytes)

View attachment "0001-disable-quirk-for-Xeon-D-1500-d2345d1231d80ecbea5fb7.patch" of type "text/x-patch" (1655 bytes)

View attachment "kern.log" of type "text/x-log" (98411 bytes)