[j:linux-intel-iotg][j:linux-intel-iot-realtime] Cannot set frame preemption

This is a public version of https://bugs.launchpad.net/bugs/2034007

[Summary]
System cannot set frame preemption via the ethtool-rt from snap store[1], will got netlink error.

[1] https://snapcraft.io/ethtool-rt

u@u-Alder-Lake-Client-Platform:~$ sudo ethtool-rt.ethtool --set-frame-preemption enp1s0 fp on
netlink error: frame preemption settings update failed
netlink error: Invalid argument
u@u-Alder-Lake-Client-Platform:~$ echo $?
81
u@u-Alder-Lake-Client-Platform:~$ sudo ethtool-rt.ethtool --show-frame-preemption enp1s0
Frame preemption settings for enp1s0:
enabled: not enabled
additional fragment size: 0
verified: 0
verification disabled: 1

[Steps to reproduce]
1. sudo snap install ethtool-ty --devmode --edge
2.sudo ethtool-rt.ethtool --set-frame-preemption {your ethernet interface} fp on
3.sudo ethtool-rt.ethtool --show-frame-preemption {your ethernet interface}

[Expected result]
Set frame preemption successfully.

[Actual result]
Got netlink error.

[Failure rate]
3/3

[Additional information]
CID: 202305-31589
SKU: ADL-S
system-manufacturer: Intel Corporation
system-product-name: Alder Lake Client Platform
bios-version: RPLISFI1.R00.4081.A05.2305241419
CPU: 12th Gen Intel(R) Core(TM) i3-12100E (8x)
GPU: 00:02.0 VGA compatible controller [0300]: Intel Corporation Device [8086:4692] (rev 0c)
kernel-version: 5.15.0-1035-intel-iot-realtime

[Stage]
Issue reported and logs collected right after it happened

----------------------

Philip Cox (philcox) wrote on 2023-09-07:   #4
After going through the code, it looks like this is caused by the variable fpcmd->add_frag_size is set to 0 and in the function igc_ethtool_set_preempt() there is the following check:

if (fpcmd->add_frag_size < 68 || fpcmd->add_frag_size > 260)
 return -EINVAL;

And this is causing the the --set-frame-preemption to fail.

ubuntu@adl-p:~$ sudo ethtool-rt.ethtool --set-frame-preemption enp169s0 fp on ; echo $?
netlink error: frame preemption settings update failed
netlink error: Invalid argument
81
ubuntu@adl-p:~$

I see in igc.h that there is a #define for IGC_I225_MIN_FRAG_SIZE_DEFAULT which is:

#define IGC_I225_MIN_FRAG_SIZE_DEFAULT 68

This is set in igc_tsn_disable_offload()

static int igc_tsn_disable_offload(struct igc_adapter *adapter)
{
...
 adapter->cycle_time = 0;
 adapter->add_frag_size = IGC_I225_MIN_FRAG_SIZE_DEFAULT;
...
}

but igc_tsn_disable_offload is not called, so the value is never set.

---------------------

Lai Jun Ann (laijunann-intel) wrote 12 hours ago: #12
0001-igc-fix-frame-preemption-not-able-to-set.patch Edit (1.3 KiB, text/plain)
The patch is ready and uploaded. Below shows the testing done with the patch:
oot@ubuntu-Alder-Lake-Client-Platform:~# ethtool --show-frame-preemption enp1s0
Frame preemption settings for enp1s0:
        enabled: enabled
        additional fragment size: 68
        verified: 0
        verification disabled: 1
root@ubuntu-Alder-Lake-Client-Platform:~#
root@ubuntu-Alder-Lake-Client-Platform:~# ethtool --set-frame-preemption enp1s0 fp off
root@ubuntu-Alder-Lake-Client-Platform:~# ethtool --show-frame-preemption enp1s0
Frame preemption settings for enp1s0:
        enabled: not enabled
        additional fragment size: 68
        verified: 0
        verification disabled: 1
root@ubuntu-Alder-Lake-Client-Platform:~# ethtool --set-frame-preemption enp1s0 fp on
root@ubuntu-Alder-Lake-Client-Platform:~# ethtool --show-frame-preemption enp1s0
Frame preemption settings for enp1s0:
        enabled: enabled
        additional fragment size: 68
        verified: 0
        verification disabled: 1

--------------

Philip Cox (philcox) wrote 20 minutes ago:   #13
I've tested the patch as well, and it works. Thanks.