.. SPDX-License-Identifier: GPL-2.0

======================================
HiSilicon PCIe Tune and Trace device
======================================

Introduction
============

HiSilicon PCIe tune and trace device (PTT) is a PCIe Root Complex
integrated Endpoint (RCiEP) device, providing the capability
to dynamically monitor and tune the PCIe link's events (tune),
and trace the TLP headers (trace). The two functions are independent,
but is recommended to use them together to analyze and enhance the
PCIe link's performance.

On Kunpeng 930 SoC, the PCIe Root Complex is composed of several
PCIe cores. Each PCIe core includes several Root Ports and a PTT
RCiEP, like below. The PTT device is capable of tuning and
tracing the links of the PCIe core.
::

          +--------------Core 0-------+
          |       |       [   PTT   ] |
          |       |       [Root Port]---[Endpoint]
          |       |       [Root Port]---[Endpoint]
          |       |       [Root Port]---[Endpoint]
    Root Complex  |------Core 1-------+
          |       |       [   PTT   ] |
          |       |       [Root Port]---[ Switch ]---[Endpoint]
          |       |       [Root Port]---[Endpoint] `-[Endpoint]
          |       |       [Root Port]---[Endpoint]
          +---------------------------+

The PTT device driver registers one PMU device for each PTT device.
The name of each PTT device is composed of 'hisi_ptt' prefix with
the id of the SICL and the Core where it locates. The Kunpeng 930
SoC encapsulates multiple CPU dies (SCCL, Super CPU Cluster) and
IO dies (SICL, Super I/O Cluster), where there's one PCIe Root
Complex for each SICL.
::

    /sys/bus/event_source/devices/hisi_ptt<sicl_id>_<core_id>

Tune
====

PTT tune is designed for monitoring and adjusting PCIe link parameters (events).
Currently we support events in 2 classes. The scope of the events
covers the PCIe core to which the PTT device belongs.

Each event is presented as a file under $(PTT PMU dir)/tune, and
a simple open/read/write/close cycle will be used to tune the event.
::

    $ cd /sys/bus/event_source/devices/hisi_ptt<sicl_id>_<core_id>/tune
    $ ls
    qos_tx_cpl    qos_tx_np    qos_tx_p
    tx_path_rx_req_alloc_buf_level
    tx_path_tx_req_alloc_buf_level
    $ cat qos_tx_dp
    1
    $ echo 2 > qos_tx_dp
    $ cat qos_tx_dp
    2

Current value (numerical value) of the event can be simply read
from the file, and the desired value written to the file to tune.

1. Tx Path QoS Control
------------------------

The following files are provided to tune the QoS of the tx path of
the PCIe core.

- qos_tx_cpl: weight of Tx completion TLPs
- qos_tx_np: weight of Tx non-posted TLPs
- qos_tx_p: weight of Tx posted TLPs

The weight influences the proportion of certain packets on the PCIe link.
For example, for the storage scenario, increase the proportion
of the completion packets on the link to enhance the performance as
more completions are consumed.

The available tune data of these events is [0, 1, 2].
Writing a negative value will return an error, and out of range
values will be converted to 2. Note that the event value just
indicates a probable level, but is not precise.

2. Tx Path Buffer Control
-------------------------

Following files are provided to tune the buffer of tx path of the PCIe core.

- rx_alloc_buf_level: watermark of Rx requested
- tx_alloc_buf_level: watermark of Tx requested

These events influence the watermark of the buffer allocated for each
type. Rx means the inbound while Tx means outbound. The packets will
be stored in the buffer first and then transmitted either when the
watermark reached or when timed out. For a busy direction, you should
increase the related buffer watermark to avoid frequently posting and
thus enhance the performance. In most cases just keep the default value.

The available tune data of above events is [0, 1, 2].
Writing a negative value will return an error, and out of range
values will be converted to 2. Note that the event value just
indicates a probable level, but is not precise.

Trace
=====

PTT trace is designed for dumping the TLP headers to the memory, which
can be used to analyze the transactions and usage condition of the PCIe
Link. You can choose to filter the traced headers by either Requester ID,
or those downstream of a set of Root Ports on the same core of the PTT
device. It's also supported to trace the headers of certain type and of
certain direction.

You can use the perf command `perf record` to set the parameters, start
trace and get the data. It's also supported to decode the trace
data with `perf report`. The control parameters for trace is inputted
as event code for each events, which will be further illustrated later.
An example usage is like
::

    $ perf record -e hisi_ptt0_2/filter=0x80001,type=1,direction=1,
      format=1/ -- sleep 5

This will trace the TLP headers downstream root port 0000:00:10.1 (event
code for event 'filter' is 0x80001) with type of posted TLP requests,
direction of inbound and traced data format of 8DW.

1. Filter
---------

The TLP headers to trace can be filtered by the Root Ports or the Requester ID
of the Endpoint, which are located on the same core of the PTT device. You can
set the filter by specifying the `filter` parameter which is required to start
the trace. The parameter value is 20 bit. Bit 19 indicates the filter type.
1 for Root Port filter and 0 for Requester filter. Bit[15:0] indicates the
filter value. The value for a Root Port is a mask of the core port id which is
calculated from its PCI Slot ID as (slotid & 7) * 2. The value for a Requester
is the Requester ID (Device ID of the PCIe function). Bit[18:16] is currently
reserved for extension.

For example, if the desired filter is Endpoint function 0000:01:00.1 the filter
value will be 0x00101. If the desired filter is Root Port 0000:00:10.0 then
then filter value is calculated as 0x80001.

The driver also presents every supported Root Port and Requester filter through
sysfs. Each filter will be an individual file with name of its related PCIe
device name (domain:bus:device.function). The files of Root Port filters are
under $(PTT PMU dir)/root_port_filters and files of Requester filters
are under $(PTT PMU dir)/requester_filters.

Note that multiple Root Ports can be specified at one time, but only one
Endpoint function can be specified in one trace. Specifying both Root Port
and function at the same time is not supported. Driver maintains a list of
available filters and will check the invalid inputs.

The available filters will be dynamically updated, which means you will always
get correct filter information when hotplug events happen, or when you manually
remove/rescan the devices.

2. Type
-------

You can trace the TLP headers of certain types by specifying the `type`
parameter, which is required to start the trace. The parameter value is
8 bit. Current supported types and related values are shown below:

- 8'b00000001: posted requests (P)
- 8'b00000010: non-posted requests (NP)
- 8'b00000100: completions (CPL)

You can specify multiple types when tracing inbound TLP headers, but can only
specify one when tracing outbound TLP headers.

3. Direction
------------

You can trace the TLP headers from certain direction, which is relative
to the Root Port or the PCIe core, by specifying the `direction` parameter.
This is optional and the default parameter is inbound. The parameter value
is 4 bit. When the desired format is 4DW, directions and related values
supported are shown below:

- 4'b0000: inbound TLPs (P, NP, CPL)
- 4'b0001: outbound TLPs (P, NP, CPL)
- 4'b0010: outbound TLPs (P, NP, CPL) and inbound TLPs (P, NP, CPL B)
- 4'b0011: outbound TLPs (P, NP, CPL) and inbound TLPs (CPL A)

When the desired format is 8DW, directions and related values supported are
shown below:

- 4'b0000: reserved
- 4'b0001: outbound TLPs (P, NP, CPL)
- 4'b0010: inbound TLPs (P, NP, CPL B)
- 4'b0011: inbound TLPs (CPL A)

Inbound completions are classified into two types:

- completion A (CPL A): completion of CHI/DMA/Native non-posted requests, except for CPL B
- completion B (CPL B): completion of DMA remote2local and P2P non-posted requests

4. Format
--------------

You can change the format of the traced TLP headers by specifying the
`format` parameter. The default format is 4DW. The parameter value is 4 bit.
Current supported formats and related values are shown below:

- 4'b0000: 4DW length per TLP header
- 4'b0001: 8DW length per TLP header

The traced TLP header format is different from the PCIe standard.

When using the 8DW data format, the entire TLP header is logged
(Header DW0-3 shown below). For example, the TLP header for Memory
Reads with 64-bit addresses is shown in PCIe r5.0, Figure 2-17;
the header for Configuration Requests is shown in Figure 2.20, etc.

In addition, 8DW trace buffer entries contain a timestamp and
possibly a prefix for a PASID TLP prefix (see Figure 6-20, PCIe r5.0).
Otherwise this field will be all 0.

The bit[31:11] of DW0 is always 0x1fffff, which can be
used to distinguish the data format. 8DW format is like
::

    bits [                 31:11                 ][       10:0       ]
         |---------------------------------------|-------------------|
     DW0 [                0x1fffff               ][ Reserved (0x7ff) ]
     DW1 [                       Prefix                              ]
     DW2 [                     Header DW0                            ]
     DW3 [                     Header DW1                            ]
     DW4 [                     Header DW2                            ]
     DW5 [                     Header DW3                            ]
     DW6 [                   Reserved (0x0)                          ]
     DW7 [                        Time                               ]

When using the 4DW data format, DW0 of the trace buffer entry
contains selected fields of DW0 of the TLP, together with a
timestamp.  DW1-DW3 of the trace buffer entry contain DW1-DW3
directly from the TLP header.

4DW format is like
::

    bits [31:30] [ 29:25 ][24][23][22][21][    20:11   ][    10:0    ]
         |-----|---------|---|---|---|---|-------------|-------------|
     DW0 [ Fmt ][  Type  ][T9][T8][TH][SO][   Length   ][    Time    ]
     DW1 [                     Header DW1                            ]
     DW2 [                     Header DW2                            ]
     DW3 [                     Header DW3                            ]

5. Memory Management
--------------------

The traced TLP headers will be written to the memory allocated
by the driver. The hardware accepts 4 DMA address with same size,
and writes the buffer sequentially like below. If DMA addr 3 is
finished and the trace is still on, it will return to addr 0.
::

    +->[DMA addr 0]->[DMA addr 1]->[DMA addr 2]->[DMA addr 3]-+
    +---------------------------------------------------------+

Driver will allocate each DMA buffer of 4MiB. The finished buffer
will be copied to the perf AUX buffer allocated by the perf core.
Once the AUX buffer is full while the trace is still on, driver
will commit the AUX buffer first and then apply for a new one with
the same size. The size of AUX buffer is default to 16MiB. User can
adjust the size by specifying the `-m` parameter of the perf command.

6. Decoding
-----------

You can decode the traced data with `perf report -D` command (currently
only support to dump the raw trace data). The traced data will be decoded
according to the format described previously (take 8DW as an example):
::

    [...perf headers and other information]
    . ... HISI PTT data: size 4194304 bytes
    .  00000000: 00 00 00 00                                 Prefix
    .  00000004: 01 00 00 60                                 Header DW0
    .  00000008: 0f 1e 00 01                                 Header DW1
    .  0000000c: 04 00 00 00                                 Header DW2
    .  00000010: 40 00 81 02                                 Header DW3
    .  00000014: 33 c0 04 00                                 Time
    .  00000020: 00 00 00 00                                 Prefix
    .  00000024: 01 00 00 60                                 Header DW0
    .  00000028: 0f 1e 00 01                                 Header DW1
    .  0000002c: 04 00 00 00                                 Header DW2
    .  00000030: 40 00 81 02                                 Header DW3
    .  00000034: 02 00 00 00                                 Time
    .  00000040: 00 00 00 00                                 Prefix
    .  00000044: 01 00 00 60                                 Header DW0
    .  00000048: 0f 1e 00 01                                 Header DW1
    .  0000004c: 04 00 00 00                                 Header DW2
    .  00000050: 40 00 81 02                                 Header DW3
    [...]