ath10k: Incorrect MTU size for SDIO

[Fabio Estevam]

Hi,

On a i.MX7-based board with QCA9377 chip, I received the following
report from a user running kernel 5.10.48:

"Doing scp or just pipe through files with >10 lines I get stalls and
error logs. The ath10k_sdio errors look like this:
[  196.822363] ath10k_sdio mmc2:0001:1: failed to transmit packet, dropping: -12
[  196.830109] ath10k_sdio mmc2:0001:1: failed to submit frame: -12
[  196.836279] ath10k_sdio mmc2:0001:1: failed to push frame: -12
[  196.925452] ath10k_sdio mmc2:0001:1: failed to transmit packet, dropping: -12
[  196.933090] ath10k_sdio mmc2:0001:1: failed to submit frame: -12
[  196.939334] ath10k_sdio mmc2:0001:1: failed to push frame: -12

I am able to reliably reproduce the issue by sending a lot of data
from the i.MX7 board to a host connected via the AP:
printf '=%.0s' {1..24000} | nc 192.168.0.2 1234

I was able to narrow the issue down to the mtu. If I set the mtu for
the wlan0 device to 1486 instead of 1500, the issue does not happen.

The size of frames that I see on Wireshark is exactly 1500 after
setting it to 1486."

Is this a known issue?

Alagu/Erik,

Have you ever observed such an issue?

Thanks