mirror of
https://github.com/torvalds/linux.git
synced 2024-11-25 21:51:40 +00:00
a588332fba
There are some warnings with this file:
/Documentation/PCI/boot-interrupts.rst:42: WARNING: Unexpected indentation.
/Documentation/PCI/boot-interrupts.rst:52: WARNING: Block quote ends without a blank line; unexpected unindent.
/Documentation/PCI/boot-interrupts.rst:92: WARNING: Unexpected indentation.
/Documentation/PCI/boot-interrupts.rst:98: WARNING: Unexpected indentation.
/Documentation/PCI/boot-interrupts.rst:136: WARNING: Unexpected indentation.
It turns that this file conversion to ReST could be improved,
in order to remove the warnings and provide a better output.
So, fix the warnings by adjusting blank lines, add a table and
some list markups. Also, mark endnodes as such.
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/a6a9eb16eede10731bcce69a600ab12d92e6ba47.1586881715.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
160 lines
6.2 KiB
ReStructuredText
160 lines
6.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
===============
|
|
Boot Interrupts
|
|
===============
|
|
|
|
:Author: - Sean V Kelley <sean.v.kelley@linux.intel.com>
|
|
|
|
Overview
|
|
========
|
|
|
|
On PCI Express, interrupts are represented with either MSI or inbound
|
|
interrupt messages (Assert_INTx/Deassert_INTx). The integrated IO-APIC in a
|
|
given Core IO converts the legacy interrupt messages from PCI Express to
|
|
MSI interrupts. If the IO-APIC is disabled (via the mask bits in the
|
|
IO-APIC table entries), the messages are routed to the legacy PCH. This
|
|
in-band interrupt mechanism was traditionally necessary for systems that
|
|
did not support the IO-APIC and for boot. Intel in the past has used the
|
|
term "boot interrupts" to describe this mechanism. Further, the PCI Express
|
|
protocol describes this in-band legacy wire-interrupt INTx mechanism for
|
|
I/O devices to signal PCI-style level interrupts. The subsequent paragraphs
|
|
describe problems with the Core IO handling of INTx message routing to the
|
|
PCH and mitigation within BIOS and the OS.
|
|
|
|
|
|
Issue
|
|
=====
|
|
|
|
When in-band legacy INTx messages are forwarded to the PCH, they in turn
|
|
trigger a new interrupt for which the OS likely lacks a handler. When an
|
|
interrupt goes unhandled over time, they are tracked by the Linux kernel as
|
|
Spurious Interrupts. The IRQ will be disabled by the Linux kernel after it
|
|
reaches a specific count with the error "nobody cared". This disabled IRQ
|
|
now prevents valid usage by an existing interrupt which may happen to share
|
|
the IRQ line::
|
|
|
|
irq 19: nobody cared (try booting with the "irqpoll" option)
|
|
CPU: 0 PID: 2988 Comm: irq/34-nipalk Tainted: 4.14.87-rt49-02410-g4a640ec-dirty #1
|
|
Hardware name: National Instruments NI PXIe-8880/NI PXIe-8880, BIOS 2.1.5f1 01/09/2020
|
|
Call Trace:
|
|
|
|
<IRQ>
|
|
? dump_stack+0x46/0x5e
|
|
? __report_bad_irq+0x2e/0xb0
|
|
? note_interrupt+0x242/0x290
|
|
? nNIKAL100_memoryRead16+0x8/0x10 [nikal]
|
|
? handle_irq_event_percpu+0x55/0x70
|
|
? handle_irq_event+0x4f/0x80
|
|
? handle_fasteoi_irq+0x81/0x180
|
|
? handle_irq+0x1c/0x30
|
|
? do_IRQ+0x41/0xd0
|
|
? common_interrupt+0x84/0x84
|
|
</IRQ>
|
|
|
|
handlers:
|
|
irq_default_primary_handler threaded usb_hcd_irq
|
|
Disabling IRQ #19
|
|
|
|
|
|
Conditions
|
|
==========
|
|
|
|
The use of threaded interrupts is the most likely condition to trigger
|
|
this problem today. Threaded interrupts may not be reenabled after the IRQ
|
|
handler wakes. These "one shot" conditions mean that the threaded interrupt
|
|
needs to keep the interrupt line masked until the threaded handler has run.
|
|
Especially when dealing with high data rate interrupts, the thread needs to
|
|
run to completion; otherwise some handlers will end up in stack overflows
|
|
since the interrupt of the issuing device is still active.
|
|
|
|
Affected Chipsets
|
|
=================
|
|
|
|
The legacy interrupt forwarding mechanism exists today in a number of
|
|
devices including but not limited to chipsets from AMD/ATI, Broadcom, and
|
|
Intel. Changes made through the mitigations below have been applied to
|
|
drivers/pci/quirks.c
|
|
|
|
Starting with ICX there are no longer any IO-APICs in the Core IO's
|
|
devices. IO-APIC is only in the PCH. Devices connected to the Core IO's
|
|
PCIe Root Ports will use native MSI/MSI-X mechanisms.
|
|
|
|
Mitigations
|
|
===========
|
|
|
|
The mitigations take the form of PCI quirks. The preference has been to
|
|
first identify and make use of a means to disable the routing to the PCH.
|
|
In such a case a quirk to disable boot interrupt generation can be
|
|
added. [1]_
|
|
|
|
Intel® 6300ESB I/O Controller Hub
|
|
Alternate Base Address Register:
|
|
BIE: Boot Interrupt Enable
|
|
|
|
== ===========================
|
|
0 Boot interrupt is enabled.
|
|
1 Boot interrupt is disabled.
|
|
== ===========================
|
|
|
|
Intel® Sandy Bridge through Sky Lake based Xeon servers:
|
|
Coherent Interface Protocol Interrupt Control
|
|
dis_intx_route2pch/dis_intx_route2ich/dis_intx_route2dmi2:
|
|
When this bit is set. Local INTx messages received from the
|
|
Intel® Quick Data DMA/PCI Express ports are not routed to legacy
|
|
PCH - they are either converted into MSI via the integrated IO-APIC
|
|
(if the IO-APIC mask bit is clear in the appropriate entries)
|
|
or cause no further action (when mask bit is set)
|
|
|
|
In the absence of a way to directly disable the routing, another approach
|
|
has been to make use of PCI Interrupt pin to INTx routing tables for
|
|
purposes of redirecting the interrupt handler to the rerouted interrupt
|
|
line by default. Therefore, on chipsets where this INTx routing cannot be
|
|
disabled, the Linux kernel will reroute the valid interrupt to its legacy
|
|
interrupt. This redirection of the handler will prevent the occurrence of
|
|
the spurious interrupt detection which would ordinarily disable the IRQ
|
|
line due to excessive unhandled counts. [2]_
|
|
|
|
The config option X86_REROUTE_FOR_BROKEN_BOOT_IRQS exists to enable (or
|
|
disable) the redirection of the interrupt handler to the PCH interrupt
|
|
line. The option can be overridden by either pci=ioapicreroute or
|
|
pci=noioapicreroute. [3]_
|
|
|
|
|
|
More Documentation
|
|
==================
|
|
|
|
There is an overview of the legacy interrupt handling in several datasheets
|
|
(6300ESB and 6700PXH below). While largely the same, it provides insight
|
|
into the evolution of its handling with chipsets.
|
|
|
|
Example of disabling of the boot interrupt
|
|
------------------------------------------
|
|
|
|
- Intel® 6300ESB I/O Controller Hub (Document # 300641-004US)
|
|
5.7.3 Boot Interrupt
|
|
https://www.intel.com/content/dam/doc/datasheet/6300esb-io-controller-hub-datasheet.pdf
|
|
|
|
- Intel® Xeon® Processor E5-1600/2400/2600/4600 v3 Product Families
|
|
Datasheet - Volume 2: Registers (Document # 330784-003)
|
|
6.6.41 cipintrc Coherent Interface Protocol Interrupt Control
|
|
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-v3-datasheet-vol-2.pdf
|
|
|
|
Example of handler rerouting
|
|
----------------------------
|
|
|
|
- Intel® 6700PXH 64-bit PCI Hub (Document # 302628)
|
|
2.15.2 PCI Express Legacy INTx Support and Boot Interrupt
|
|
https://www.intel.com/content/dam/doc/datasheet/6700pxh-64-bit-pci-hub-datasheet.pdf
|
|
|
|
|
|
If you have any legacy PCI interrupt questions that aren't answered, email me.
|
|
|
|
Cheers,
|
|
Sean V Kelley
|
|
sean.v.kelley@linux.intel.com
|
|
|
|
.. [1] https://lore.kernel.org/r/12131949181903-git-send-email-sassmann@suse.de/
|
|
.. [2] https://lore.kernel.org/r/12131949182094-git-send-email-sassmann@suse.de/
|
|
.. [3] https://lore.kernel.org/r/487C8EA7.6020205@suse.de/
|