Provided by: pciutils_3.13.0-2_amd64 
NAME
pcilmr - margin PCIe Links
SYNOPSIS
pcilmr [--margin] [<common options>] <link port> [<link options>] [<link port> [<link options>] ...]
pcilmr --full [<common options>]
pcilmr --scan
CONFIGURATION
List of the requirements for links and system settings to run the margining test.
BIOS settings (depends on the system, relevant for server baseboards with Xeon CPUs):
• Turn off PCIe Leaky Bucket Feature, Re-Equalization and Link Degradation;
• Set Error Thresholds to 0;
• Intel VMD for NVMe SSDs - in case of strange behavior of the pcilmr, try to run it with the VMD turned
off.
Device (link) requirements:
Configured by the user before running the utility, the utility does not change them:
• The current Link data rate must be 16.0 GT/s or higher (right now utility supports 16 GT/s and
32 GT/s Links);
• Link Downstream Component must be at D0 Power Management State.
Configured by the utility during operation, utility set them to their original state after
receiving the results:
• The ASPM must be disabled in both the Downstream Port and Upstream Port;
• The Hardware Autonomous Speed Disable bit of the Link Control 2 register must be Set in both
the Downstream Port and Upstream Port;
• The Hardware Autonomous Width Disable bit of the Link Control register must be Set in both the
Downstream Port and Upstream Port.
DESCRIPTION
pcilmr utility allows you to take advantage of the PCIe Lane Margining at the Receiver capability which
is mandatory for all Ports supporting a data rate of 16.0 GT/s or higher, including Pseudo Ports
(Retimers). Lane Margining at Receiver enables system software to obtain the margin information of a
given Receiver while the Link is in the L0 state. The margin information includes both voltage and time,
in either direction from the current Receiver position. Margining support for timing is required, while
support for voltage is optional at 16.0 GT/s and required at 32.0 GT/s and higher data rates. Also,
independent time margining and independent voltage margining is optional.
Utility allows to get an approximation of the eye margin diagram in the form of a rhombus (by four
points). Lane Margining at the Receiver capability enables users to margin PCIe links without a hardware
debugger and without the need to stop the target system. Utility can be useful to debug link issues due
to receiver margins.
pcilmr requires root privileges (to access Extended Configuration Space), but during our testing there
were no problems with the devices and they successfully returned to their normal initial state after the
end of testing.
RESULTS GRADING
The PCIe specification provides reference values for the eye diagram, which are also used by the pcilmr
to evaluate the results, but it seems that it makes sense to contact the manufacturer of a particular
device for references.
The utility uses values set in PCIe Base Spec Rev. 5.0 Section 8.4.2 as the default eye width and height
minimum references. Recommended values were taken from the PCIe Architecture PHY Test Spec Rev 5.0
(Transmitter Electrical Compliance).
Reference grading values currently used by the utility are presented in the table below:
┌─────┬─────────────────────┬──────────────────────┐
--
HARDWARE QUIRKS SUPPORT
Thanks to testing or directly from the manufacturer's documentation, we know that some devices require
special treatment during the margining. Utility detects such devices based on their Vendor ID - Device
ID pair. Right now the list of special devices is hardcoded in margin_hw file. For such devices utility
can automatically adjust port margining parameters or grading options.
For example, for Ice Lake CPUs RC ports pcilmr will change device MaxVoltageOffset value and will force
the use of 'one side is the whole' grading mode.
OPTIONS
Device Specifier
You can specify Downstream or Upstream Port of the Link.
<device/component>
[<domain>:]<bus>:<dev>.<func> (see lspci(8))
Utility Modes
--margin <downstream component> ...
Margin selected Links.
--full Margin all ready for testing (in a meaning similar to the --scan option) Links in the system (one
by one).
--scan Scan for Links with negotiated speed 16 GT/s or higher. Mark "Ready" those of them in which at
least one of the Link sides have Margining Ready bit set meaning that these Links are ready for
testing and you can run utility on them.
Margining Common (for all specified links) options
-c Print Device Lane Margining Capabilities only. Do not run margining.
-e <errors>
Specify Error Count Limit for margining.
Default: 4.
-o <directory>
Save margining results in csv form into the specified directory. Utility will generate file with
the name in form of "lmr_<port>_Rx#_<timestamp>.csv" for each successfully tested receiver.
-d <time>
Specify dwell time in seconds for the margining step.
Default: 1 s
Margining Link specific options
-l <lane>[,<lane>...]
®.br Remember that Device may use Lane Reversal for Lane numbering. However, utility uses logical
lane numbers in arguments and for logging. Utility will automatically determine Lane Reversal and
tune its calls.
Default: all link lanes.
-r <recvn>[,<recvn>...]
Specify Receivers to select margining targets.
Default: all available Receivers (including Retimers).
-p <parallel_lanes>
Specify number of lanes to margin simultaneously.
According to spec it's possible for Receiver to margin up to MaxLanes + 1 lanes simultaneously,
but during testing, performing margining on several lanes simultaneously led to results that were
different from sequential margining, so this feature requires additional verification and -p
option right now is for experiments mostly.
Default: 1.
Use only one of -T/-t options at the same time (same for -V/-v).
Without these options utility will use MaxSteps from Device capabilities as test limit.
-T Time Margining will continue until the Error Count is no more than an Error Count Limit. Use this
option to find Link limit.
-t <steps>
Specify maximum number of steps for Time Margining.
-V Same as -T option, but for Voltage.
-v <steps>
Specify maximum number of steps for Voltage Margining.
-g <recvn>t=<criteria>{%|ps}[,f]
<recvn>t=f[,<criteria>{%|ps}]
<recvn>v=<criteria>[,f]
<recvn>v=f[,<criteria>]
Specify pass/fail grading criteria for eye width (timing - t) or height (voltage - v) for one of
the link receivers. For EW you must choose one of the units (% UI or ps), for EH mV is used.
Additional flag f is for situations when port doesn't support two side independent margining. In
such cases by default utility will calculate EW or EH as a double one side result. You can add f
flag for -g option to tell the utility that the result in one direction is actually the
measurement of the full eye and it does not need to be multiplied. This is so called 'one side is
the whole' grading mode.
EXAMPLES
Utility syntax example:
pcilmr -o csv ab:0.0 -r 1,6 -g 1t=20% -g 1v=f,30 52:0.0 -l 0,1,2 -TV
Examples of collected results on different systems.
SEE ALSO
lspci(8), PCI Express Base Specification (Lane Margining at Receiver)
pciutils-3.13.0 30 May 2024 PCILMR(8)