This still seems to be broken (I'm also using the 955Q). Is it possibly related to this revert? This tuner did always list two adapters in TVHeadend. This is a real bummer, I think that particular tuner was one of the cheapest supported tuners.
Here's another dmesg log with a stack trace from TVHeadend trying to use the dvb driver, looks like:
[ 12.935031] si2157 7-0060: found a 'Silicon Labs Si2157-A30'
[ 12.983778] si2157 7-0060: firmware version: 3.0.5
[ 12.983840] Unable to handle kernel paging request at virtual address a8c33800
[ 12.983844] pgd = a8ef0000
[ 12.983847] [a8c33800] *pgd=28c1141e(bad)
[ 12.983863] Internal error: Oops: 8000000d [#1] SMP ARM
[ 12.983883] Modules linked in: veth hci_uart btbcm bluetooth ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype iptable_filter ip_tables xt_conntrack x_tables nf_nat nf_conntrack br_netfilter bridge stp llc overlay si2157(O) lgdt3306a cx231xx_dvb_ci(O) tas2101(O) dvb_core(O) 8021q fuse cx25840(O) cx231xx(O) videobuf_vmalloc(O) videobuf_core(O) cx2341x(O) tveeprom(O) brcmfmac i2c_mux v4l2_common(O) brcmutil videodev(O) cfg80211 rc_core(O) rfkill bcm2835_gpiomem fixed
[ 12.984006] CPU: 2 PID: 658 Comm: tvheadend Tainted: G O 4.9.59 #1
[ 12.984015] Hardware name: BCM2835
[ 12.984022] task: a8db3900 task.stack: a8cc6000
[ 12.984033] PC is at 0xa8c33800
[ 12.984056] LR is at dvb_frontend_ioctl_properties+0x6e0/0xd18 [dvb_core]
[ 12.984067] pc : [<a8c33800>] lr : [<7f5081ec>] psr: a0090113
[ 12.984067] sp : a8cc7c00 ip : a8cc7b88 fp : a8cc7e0c
[ 12.984081] r10: a2176200 r9 : 00000000 r8 : ae0a0780
[ 12.984089] r7 : a8cc7e40 r6 : 00000000 r5 : a8c33808 r4 : a2176200
[ 12.984098] r3 : a8c33800 r2 : 00000000 r1 : a2176200 r0 : a8c33808
[ 12.984109] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
[ 12.984119] Control: 10c5383d Table: 28ef006a DAC: 00000055
[ 12.984127] Process tvheadend (pid: 658, stack limit = 0xa8cc6210)
[ 12.984137] Stack: (0xa8cc7c00 to 0xa8cc8000)
[ 12.984148] 7c00: a8cc7c4c a8cc7c10 8017c47c 805826e4 0005fe3d 00000000 00000006 00000002
[ 12.984161] 7c20: 00000001 00000000 00000009 00000002 00000000 00000004 00000004 00000000
[ 12.984173] 7c40: 00000009 00000009 00000002 00000006 00000000 00000000 00000000 00000000
[ 12.984199] 7c60: 00000000 00000000 00000000 00000009 00000006 00000000 00000000 00000009
[ 12.984223] 7c80: 00000006 00000000 00000000 00000009 00000006 00000000 ffffffff ffffffff
[ 12.984248] 7ca0: 00000000 00000000 00000000 00000000 ffffffff 00000001 00000000 00000000
[ 12.984272] 7cc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984296] 7ce0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984320] 7d00: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984345] 7d20: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984369] 7d40: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984393] 7d60: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984417] 7d80: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984442] 7da0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 12.984466] 7dc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000002
[ 12.984491] 7de0: a8cc7e0c 80086f53 ade1d598 ae0a0780 a8c33808 a8cc7e40 00000000 ae0a0780
[ 12.984516] 7e00: a8cc7e34 a8cc7e10 7f5088f8 7f507b18 80086f53 00000008 00000002 7eaae83c
[ 12.984541] 7e20: a8cc7e40 00000000 a8cc7eec a8cc7e38 7f4fe8a0 7f508830 807c5f64 7f508824
[ 12.984565] 7e40: 00000001 7eaae8b4 00000041 00000000 00000000 00000006 00000002 00000002
[ 12.984590] 7e60: a8e23b48 ae8eb210 aa451d48 a8cc7e78 80203f68 80203be0 00000000 00000013
[ 12.984616] 7e80: a8cc7ea8 a8cc7f5c 00000001 80107b84 a8cc6000 00000000 a8cc7f4c a8cc7ea8
[ 12.984641] 7ea0: 802049e4 801fe5b4 ae8eb210 aa451d48 8c730ef0 00000009 aa0ce022 a8cc7ec8
[ 12.984665] 7ec0: 00000000 7eaae83c a8e23b48 ae0a0780 00000013 7eaae83c a8cc6000 00000000
[ 12.984690] 7ee0: a8cc7efc a8cc7ef0 7f4fe984 7f4fe7f4 a8cc7f7c a8cc7f00 80206f44 7f4fe968
[ 12.984715] 7f00: 80213528 806cf2e0 80213354 aa0ce000 ae0a0780 aa0ce000 00000020 ae0a0788
[ 12.984740] 7f20: a8e23b48 00000000 a8cc7f54 a8cc7f38 80213880 806d2a5c 00000013 7eaae8b4
[ 12.984765] 7f40: 00000013 00000001 80086f53 7eaae83c a8cc7f6c ae0a0781 00000013 ae0a0780
[ 12.984790] 7f60: 80086f53 7eaae83c a8cc6000 00000000 a8cc7fa4 a8cc7f80 802076e4 80206ea8
[ 12.984816] 7f80: 7eaae8b4 7eaae848 00000001 00000036 80107b84 a8cc6000 00000000 a8cc7fa8
[ 12.984840] 7fa0: 801079e0 802076b4 7eaae8b4 7eaae848 00000013 80086f53 7eaae83c 0000002c
[ 12.984865] 7fc0: 7eaae8b4 7eaae848 00000001 00000036 7eaae83c 00000001 00000013 00000000
[ 12.984890] 7fe0: 00c56c3c 7eaae7e4 004fa2c4 76c0ccec 400f0010 00000013 2f7fa861 2f7fac61
[ 12.984910] Backtrace:
[ 12.984967] [<7f507b0c>] (dvb_frontend_ioctl_properties [dvb_core]) from [<7f5088f8>] (dvb_frontend_ioctl+0xd4/0x10c [dvb_core])
[ 12.985000] r10:ae0a0780 r9:00000000 r8:a8cc7e40 r7:a8c33808 r6:ae0a0780 r5:ade1d598
[ 12.985022] r4:80086f53
[ 12.985057] [<7f508824>] (dvb_frontend_ioctl [dvb_core]) from [<7f4fe8a0>] (dvb_usercopy+0xb8/0x174 [dvb_core])
[ 12.985084] r9:00000000 r8:a8cc7e40 r7:7eaae83c r6:00000002 r5:00000008 r4:80086f53
[ 12.985127] [<7f4fe7e8>] (dvb_usercopy [dvb_core]) from [<7f4fe984>] (dvb_generic_ioctl+0x28/0x3c [dvb_core])
[ 12.985153] r10:00000000 r9:a8cc6000 r8:7eaae83c r7:00000013 r6:ae0a0780 r5:a8e23b48
[ 12.985175] r4:7eaae83c
[ 12.985206] [<7f4fe95c>] (dvb_generic_ioctl [dvb_core]) from [<80206f44>] (do_vfs_ioctl+0xa8/0x80c)
[ 12.985234] [<80206e9c>] (do_vfs_ioctl) from [<802076e4>] (SyS_ioctl+0x3c/0x64)
[ 12.985259] r10:00000000 r9:a8cc6000 r8:7eaae83c r7:80086f53 r6:ae0a0780 r5:00000013
[ 12.985281] r4:ae0a0781
[ 12.985300] [<802076a8>] (SyS_ioctl) from [<801079e0>] (ret_fast_syscall+0x0/0x34)
[ 12.985325] r9:a8cc6000 r8:80107b84 r7:00000036 r6:00000001 r5:7eaae848 r4:7eaae8b4
[ 12.985349] Code: 15400c5d 9e223080 0e1e5039 5d6efb45 (aa2b1000)
[ 12.985367] ---[ end trace 772782b19907849d ]---