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Simplify the systems requirements section of the readme file.
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Now that PTP support support is well established, remove the text that
attempts to explain the (at the time) incomplete kernel support.  Instead
just give a couple of ethtool examples.

Signed-off-by: Richard Cochran <[email protected]>
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richardcochran committed Feb 25, 2019
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* System Requirements

In order to run this software, you need Linux kernel
version 3.0 or newer, and the kernel header files must available at
compile time.

In addition, you will also need to have either:

1. A supported Ethernet MAC device.

2. A supported PHY device paired with a MAC that allows time
stamping in the PHY (indicated by PHY=Y in the table below).

** Linux Kernel Support

In order to support PTP, the operating system needs to provide two
services: network packet time stamping and clock control. In 2009,
Patrick Ohly added a new socket option called SO_TIMESTAMPING for
packet time stamping, especially for PTP. This work appeared in
Linux version 2.6.30.

In July of 2011, the PTP Hardware Clock (PHC) subsystem was merged
into Linux version 3.0. The PHC code provides a driver framework and
the user space API for clock control.

** Ethtool Support

Starting with version 3.5 of the Linux kernel, you can query the
time stamping capabilities of a network interface using the
ETHTOOL_GET_TS_INFO ioctl. Using ethtool version 3.4 or later, you
can check your system's time stamping support as shown in the
following example.
In order to run this software, you need Linux kernel version 3.0 or
newer. Check whether your network interface supports PTP with the
following command.

#+BEGIN_EXAMPLE
ethtool -T eth0
#+END_EXAMPLE

If the ethtool ioctl is available, then the ptp4l program will use
it in order to discover the proper PHC device.

** Driver Support Matrix

The following two tables list the drivers that support the PHC
subsystem and the Linux kernel version when they first appeared.
These drivers will create a PHC device for controlling the hardware
clock.

*** Hardware Timestamping - PHY

|---------+-------------------------------+---------|
| Driver | Hardware | Version |
|---------+-------------------------------+---------|
| dp83640 | National Semiconductor PHYTER | 3.0 |
|---------+-------------------------------+---------|

*** Hardware Timestamping - MAC

|------------+--------------------------+---------|
| Driver | Hardware | Version |
|------------+--------------------------+---------|
| amd-xgbe | AMD 10GbE Ethernet Soc | 3.17 |
| bfin_mac | Analog Blackfin | 3.8 |
| bnx2x | Broadcom NetXtremeII 10G | 3.18 |
| cpts | Texas Instruments am335x | 3.8 |
| e1000e | Intel 82574, 82583 | 3.9 |
| fm10k | Intel FM10000 | 3.18 |
| fec | Freescale i.mx6 | 3.8 |
| gianfar | Freescale eTSEC PowerPC | 3.0 |
| i40e | Intel XL710 Family | 3.14 |
| igb | Intel 82576, 82580 | 3.5 |
| ixgbe | Intel 82599 | 3.5 |
| mlx4 | Mellanox 40G PCI | 3.14 |
| ptp_ixp46x | Intel IXP465 | 3.0 |
| ptp_phc | Lapis EG20T PCH | 3.5 |
| sfc | Solarflare SFC9000 | 3.7 |
| stmmac | STM Synopsys IP Core | 3.10 |
| tg3 | Broadcom Tigon3 PCI | 3.8 |
| tilegx | Tilera GBE/XGBE | 3.12 |
|------------+--------------------------+---------|

*** Software Timestamping

The table below shows the Linux drivers that support software time
stamping. In addition, the 'PHY' column indicates whether the
Ethernet MAC driver can support a PTP Hardware Clock in an
external PHY. The letter 'Y' in this column means that if you
design a mother board that combines such a MAC with a PTP capable
PHY, then it will work with the Linux PHC subsystem.

|--------------+--------------------------+---------+-----|
| Driver | Hardware | Version | PHY |
|--------------+--------------------------+---------+-----|
| 3c59x | 3Com EtherLink PCI | 3.14 | N |
| altera_tse | Altera Triple-Speed MAC | 3.15 | Y |
| bna | Brocade 1010/1020 10Gb | 3.14 | N |
| bnx2x | Broadcom Everest | 3.5 | N |
| davinci_emac | TI DaVinci, Sitara | 3.1 | Y |
| dnet | Dave Ethernet MAC | 3.1 | Y |
| e100 | Intel PRO/100 | 3.5 | N |
| e1000 | Intel PRO/1000 PCI/PCI-X | 3.5 | N |
| e1000e | Intel PRO/1000 PCIe | 3.5 | N |
| emaclite | Xilinx Ethernet Lite | 3.1 | Y |
| ethoc | OpenCores 10/100 MAC | 3.1 | Y |
| fec | Freescale Coldfire | 3.1 | Y |
| fec_mpc52xx | Freescale MPC5200 | 3.1 | Y |
| forcedeth | NVIDIA nForce | 3.5 | N |
| fs_enet | Freescale MPC512x | 3.1 | Y |
| genet | Broadcom GENET | 3.15 | Y |
| ixp4xx_eth | Intel IXP4xx | 3.0 | Y |
| lib8390 | Asix AX88796 | 3.1 | Y |
| lib8390 | Various 8390 based HW | 3.1 | N |
| ll_temac | Xilinx LL TEMAC | 3.1 | Y |
| macb | Atmel AT32, AT91 | 3.1 | Y |
| mv643xx_eth | Marvell Discovery, Orion | 3.1 | Y |
| pxa168_eth | Marvell pxa168 | 3.1 | Y |
| r6040 | RDC Ethernet MAC | 3.1 | Y |
| r8169 | Realtek 8169/8168/8101 | 3.4 | N |
| samsun-sxgbe | Samsung SXGBE 10G | 3.15 | Y |
| smsc911x | SMSC LAN911x, LAN921x | 3.1 | Y |
| smsc9420 | SMSC LAN9420 PCI | 3.1 | Y |
| stmmac | STM Synopsys IP Core | 3.1 | Y |
| tg3 | Broadcom Tigon3 PCI | 3.1 | Y |
| ucc_geth | Freescale QE Gigabit | 3.1 | Y |
| usbnet | USB network devices | 3.2 | Y/N |
| xgene-enet | APM X-Gene SoC | 3.17 | Y |
|--------------+--------------------------+---------+-----|

* Installation
This command shows whether a MAC supports hardware or software time
stamping. The following example output indicates support for
hardware time stamping.

** Linux kernel
#+BEGIN_EXAMPLE
Time stamping parameters for eth6:
Capabilities:
hardware-transmit (SOF_TIMESTAMPING_TX_HARDWARE)
software-transmit (SOF_TIMESTAMPING_TX_SOFTWARE)
hardware-receive (SOF_TIMESTAMPING_RX_HARDWARE)
software-receive (SOF_TIMESTAMPING_RX_SOFTWARE)
software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
hardware-raw-clock (SOF_TIMESTAMPING_RAW_HARDWARE)
PTP Hardware Clock: 1
Hardware Transmit Timestamp Modes:
off (HWTSTAMP_TX_OFF)
on (HWTSTAMP_TX_ON)
Hardware Receive Filter Modes:
none (HWTSTAMP_FILTER_NONE)
all (HWTSTAMP_FILTER_ALL)
#+END_EXAMPLE

There are many ways of getting a precompiled Linux kernel or
compiling your own, so this section is only meant as an example. It
is important to have the kernel headers available when compiling
the Linux PTP stack.
The next example shows the case where the MAC only supports software
time stamping. The ~ptp4l~ program requires either the ~-S~ command
line argument or the ~time_stamping software~ configuration option
when using such interfaces.

#+BEGIN_EXAMPLE
export ARCH=x86
export CROSS_COMPILE=
export KBUILD_OUTPUT=/home/richard/kernel/ptp_debian
mkdir -p $KBUILD_OUTPUT
cp /boot/config-2.6.38-bpo.2-686 $KBUILD_OUTPUT/.config
make oldnoconfig
make menuconfig
time make -j4
make headers_install
Time stamping parameters for enp6s0:
Capabilities:
software-transmit (SOF_TIMESTAMPING_TX_SOFTWARE)
software-receive (SOF_TIMESTAMPING_RX_SOFTWARE)
software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
PTP Hardware Clock: none
Hardware Transmit Timestamp Modes: none
Hardware Receive Filter Modes: none
#+END_EXAMPLE

Here is a table of kernel configuration options needed for PTP
support. In addtion to these, you should enable the specific
Ethernet MAC and PHY drivers for your hardware.

|---------------------------------+-----------------------------|
| Option | Description |
|---------------------------------+-----------------------------|
| CONFIG_PPS | Required |
| CONFIG_NETWORK_PHY_TIMESTAMPING | Timestamping in PHY devices |
| PTP_1588_CLOCK | PTP clock support |
|---------------------------------+-----------------------------|
Note the ~software-transmit (SOF_TIMESTAMPING_TX_SOFTWARE)~
capability. If this is lacking, then the MAC cannot be used at
all. However, adding this capability entails adding a single line
of code to the device driver.

** PTP stack
* Installation

1. Just type 'make'

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