linux-kernel - [RFC] PCI: PTM Driver

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Date:	Mon, 29 Feb 2016 07:28:52 +0000
From:	"Yong, Jonathan" <jonathan.yong@...el.com>
To:	linux-kernel@...r.kernel.org
Cc:	jonathan.yong@...el.com
Subject: [RFC] PCI: PTM Driver

Hello LKML,

This is a preliminary implementation of the PTM[1] support driver, the code
is obviously hacked together and in need of refactoring. This driver has
only been tested against a virtual PCI bus.

The drivers job is to get to every PTM capable device, set some PCI config
space bits, then go back to sleep [2].

PTM capable PCIe devices will get a new sysfs entry to allow PTM to be
enabled if automatic PTM activation is disabled, or disabled if so desired.

Comments? Should I explain the PTM registers in more details?
Please CC me, thanks.

[1] Precision Time Measurement: A protocol for synchronizing PCIe endpoint
clocks against the host clock as specified in the PCI Express Base
Specification 3.1. It is identified by the 0x001f extended capability ID.

PTM capable devices are split into 3 roles, master, responder and requester.
Summary as follows:

A master holds the master clock that will be used for all devices under its
domain (not to be confused with PCI domains). There may be multiple masters
in a PTM hierarchy, in which case, the highest master closest to the root
complex will be selected for the PTM domain. A master is also always
responder capable. Clock precision is signified by a Local Clock
Granularity field, in nano-seconds.

A responder responds to any PTM synchronization requests from a downstream
device. A responder is typically a switch device. It may also hold a local
clock signified by a non-zero Local Clock Granularity field. A value of 0
signifies that the device simply propagates timing information from
upstream devices.

A requester is typically an endpoint that will request synchronization
updates from an upstream PTM capable time source. The driver will update
the Effective Clock Granularity field based on the same field from the
PTM domain master. The field should be programed with a value of 0 if any
intervening responder has a Local Clock Granularity field value of 0.

[2] The software drivers never see the PTM packets, the PCI Express Base
Specificaton 3.1 reads:
	PTM capable components can make their PTM context available for
	inspection by software, enabling software to translate timing
	information between local times and PTM Master Time.

This isn't very informative.

Yong, Jonathan (1):
  PCI: PTM preliminary implementation

 drivers/pci/pci-sysfs.c     |   7 +
 drivers/pci/pci.h           |  21 +++
 drivers/pci/pcie/Kconfig    |   8 +
 drivers/pci/pcie/Makefile   |   2 +-
 drivers/pci/pcie/pcie_ptm.c | 353 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/pci/probe.c         |   3 +
 6 files changed, 393 insertions(+), 1 deletion(-)
 create mode 100644 drivers/pci/pcie/pcie_ptm.c

-- 
2.4.10