MyGica T230 dvb-t2 data corruption since commit 5fa8815

[James Hutchinson <jahutchinson99@googlemail.com>]

(trying again in plain text)...

I'm encountering invalid checksum errors randomly in tvheadend with my
MyGica T230 DVB-T2 tuner, straight after upgrading from Debian Stretch
(kernel 4.9.168) to Buster (kernel 4.19.37).

For example

2019-06-29 16:32:27.259 [   INFO]:subscription: 004B: "scan"
subscribing to mux "618.167MHz", weight: 6, adapter: "Silicon Labs
Si2168 #0 : DVB-T #0", network: "Freeview", service: "Raw PID
Subscription"
2019-06-29 16:32:27.769 [WARNING]:tbl-eit: uk_freeview: 618.167MHz in
Freeview: invalid checksum (len 1558, errors 1)
2019-06-29 16:32:27.770 [WARNING]:tbl-base: pat: 618.167MHz in
Freeview: invalid checksum (len 136, errors 1)
2019-06-29 16:32:27.967 [WARNING]:tbl-base: sdt: 618.167MHz in
Freeview: invalid checksum (len 971, errors 1)
2019-06-29 16:32:28.462 [WARNING]:tbl-base: pmt: 618.167MHz in
Freeview: invalid checksum (len 60, errors 1)
2019-06-29 16:32:28.463 [WARNING]:tbl-base: pmt: 618.167MHz in
Freeview: invalid checksum (len 46, errors 1)
2019-06-29 16:32:28.637 [WARNING]:tbl-base: pmt: 618.167MHz in
Freeview: invalid checksum (len 38, errors 1)
2019-06-29 16:32:32.258 [   INFO]:mpegts: 618.167MHz in Freeview scan complete
2019-06-29 16:32:32.258 [   INFO]:subscription: 004B: "scan" unsubscribing
2019-06-29 16:32:32.259 [   INFO]:mpegts: 642MHz in Freeview - tuning
on Silicon Labs Si2168 #0 : DVB-T #0
2019-06-29 16:32:32.259 [   INFO]:subscription: 004E: "scan"
subscribing to mux "642MHz", weight: 6, adapter: "Silicon Labs Si2168
#0 : DVB-T #0", network: "Freeview", service: "Raw PID Subscription"
2019-06-29 16:32:41.179 [   INFO]:mpegts: 642MHz in Freeview scan complete
2019-06-29 16:32:41.179 [   INFO]:subscription: 004E: "scan" unsubscribing
2019-06-29 16:32:41.180 [   INFO]:mpegts: 602MHz in Freeview - tuning
on Silicon Labs Si2168 #0 : DVB-T #0
2019-06-29 16:32:41.180 [   INFO]:subscription: 0052: "scan"
subscribing to mux "602MHz", weight: 6, adapter: "Silicon Labs Si2168
#0 : DVB-T #0", network: "Freeview", service: "Raw PID Subscription"
2019-06-29 16:32:41.835 [WARNING]:tbl-eit: uk_freeview: 602MHz in
Freeview: invalid checksum (len 320, errors 1)
2019-06-29 16:32:42.109 [WARNING]:tbl-base: sdt: 602MHz in Freeview:
invalid checksum (len 322, errors 1)
2019-06-29 16:32:42.314 [WARNING]:tbl-base: pmt: 602MHz in Freeview:
invalid checksum (len 84, errors 1)
2019-06-29 16:32:46.180 [   INFO]:mpegts: 602MHz in Freeview scan complete
2019-06-29 16:32:46.180 [   INFO]:subscription: 0052: "scan" unsubscribing

The issue is not specific to particular muxes, and happens entirely at
random. If I retune then the same mux will scan without issue. It also
causes data corruption when streaming with continuity counter errors
in the tvh log; again retuning often resolves the problem, but i never
had any such issues with kernel v4.9.x.

Heres the output of lsusb to confirm my hardware id:
0572:c688 Conexant Systems (Rockwell), Inc. Geniatech T230 DVB-T2 TV Stick

I've been testing various kernel versions in-between 4.9->4.19 and
quickly found that the issue was introduced somewhere between
4.9->4.10.

I therefore performed a (lengthy) git bisect to find out which of the
14,248 commits during the v4.10 development cycle introduced this
regression.

I have tracked this regression down to the following commit:
5fa8815: [media] dvb-usb-cxusb: Geniatech T230 - resync TS FIFO after lock

Indeed, if I revert that commit on an upto-date kernel, I now have a
stable MyGica T230 tuner once more.

Please note that i've tried the latest media_build drivers and have
also the 5.2 kernel; both of which have the issue, and both of which
can be fixed by reverting 5fa8815.

Regards,
James