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USB-to-UART converter dropping data #2197

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@iurly

Description

@iurly

Original post here: https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=192987
TL;DR:

  • I'm seeing sporadic data loss from a Full-Speed USB-to-UART bridge from Silabs (CP2104x) running at 2.000.000 bps (actual data traffic around 1.200.000bps)
  • Current settings (tweaking them does not make any difference though):
    dwc_otg.nak_holdoff=2 dwc_otg.fiq_enable=1 dwc_otg.fiq_fsm_enable=1 dwc_otg.fiq_fsm_mask=0x7 dwc_otg.speed=1
  • First drops occur after about 10-30 minutes
  • Identified as a regression between 4.4 and 4.9
  • Tested as working with:
    • 4.4.38, 4.4.50 (from pre-compiled release)
    • 4.8.16 (from source commit 061dccc)
  • Tested as broken with:
    • 4.9.11 (from source commit ef6bc39)
    • 4.9.37 (from pre-compiled release)
    • 4.9.48 (from pre-compiled release)
    • 4.12.11 (from source commit 8f82f55)
    • 4.13.1 (from source commit 93058c5)

I'm willing to investigate this further and provide any required input, but I can't really bisect the whole tree.
Please give me some guidance as to where to look and how I could reproduce the issue quicker.
Thank you!

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