However, if I disable firmware.rules, *but* leave persistent_v4l.rules enabled, I still get a crash on boot - probably because udev is trying to probe the hardware before ueventd has started up to handle the firmware request.

[    4.898886] msm_mctl_dev_open mctl NULL!
[    4.899221] Unable to handle kernel NULL pointer dereference at virtual address 00000238
[    4.899313] pgd = edf68000
[    4.899404] [00000238] *pgd=af5cc831, *pte=00000000, *ppte=00000000
[    4.899710] Internal error: Oops: 17 [#1] PREEMPT SMP ARM
[    4.899801] Modules linked in:
[    4.899984] CPU: 2    Not tainted  (3.4.0-1-mako #7-Ubuntu)
[    4.900076] PC is at msm_mctl_dev_close+0x1c/0x164
[    4.900137] LR is at v4l2_release+0x54/0x74
[    4.900259] pc : <c04d66d8>    lr : <c04b28d4>    psr: 60000013
[    4.900289] sp : edf1bee8  ip : edf1bf18  fp : edf1bf14
[    4.900442] r10: ee3edd80  r9 : 00000000  r8 : eefec490
[    4.900534] r7 : ef3c8d00  r6 : 00000010  r5 : ee3edd80  r4 : 00000000
[    4.900656] r3 : c04d66bc  r2 : 00000002  r1 : ee3edd80  r0 : ee3edd80
[    4.900717] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
[    4.900839] Control: 10c5787d  Table: ae96806a  DAC: 00000015
[    4.900961] 
[    4.900961] PC: 0xc04d6658:
[    4.901083] 6658  1afffff6 e594024c ebf1a9b7 e3a03000 e584324c e1a00008 e3e0700b eb0f8442
[    4.901815] 6678  ea000008 e2855001 eaffffff e5963000 e1550003 3affffd8 e5963000 e5843248
[    4.902456] 6698  e1a00008 eb0f8438 e1a00007 e89daff8 c0b6408b c0b63c39 c092def1 c0b63c50
[    4.903128] 66b8 
[    4.903189] 
[    4.903189] res_trk_download_firmware(): Request firmware download
[    4.903433]  c0b63c69 e1a0c00d e92ddff8 e24cb004 e52de004 e8bd4000 e590407c e1a0a000
[    4.904104] 66d8  e5945238 e3550000 1a000004 e59f0128 e3e07015 e59f1124 eb0f4d12 ea000044
[    4.904745] 66f8  e595041c e2858e16 eb0014ae e2849fbf e1a06000 e1a00008 eb0f849f e1a00009
[    4.905417] 6718  eb0f849d e5953174 e3530001 13a07000 1a000009 e1a00005 eb002052 e2507000
[    4.906088] 6738  a3a06000 aa000004 e59f10d0 e1a02007 e59f00cc eb0f4cfb ea00002b e3a03000
[    4.906760] 
[    4.906760] LR: 0xc04b2854:
[    4.906882] 2854  e1a00005 e89da878 e3000145 e89da878 e1a0c00d e92dd800 e24cb004 e52de004
[    4.907584] 2874  e8bd4000 ebf23931 e89da800 e1a0c00d e92dd830 e24cb004 e52de004 e8bd4000
[    4.908194] 2894  e1a00001 e1a05001 ebffff7e e5903050 e1a04000 e5933024 e3530000 0a00000b
[    4.908805] 28b4  e5900250 e3500000 0a000000 eb101433 e5943050 e1a00005 e5933024 e12fff33
[    4.909476] 28d4  e5940250 e3500000 0a000000 eb1013a7 e2840058 ebfbcc6b e3a00000 e89da830
[    4.910148] 28f4  e1a0c00d e92dd878 e24cb004 e52de004 e8bd4000 e1a06000 e1a05001 ebffff61
[    4.910819] 2914  e5903050 e1a04000 e593301c e3530000 0a000016 e5900250 e3500000 1a000004
[    4.911490] 2934  e5943220 e3130001 03e05012 0a00000a ea000003 eb101337 e3500000 0afffff7
[    4.912162] 
[    4.912162] SP: 0xedf1be68:
[    4.912284] be68  c08bc3b4 c0096d28 ef08ec40 c04d66d8 60000013 ffffffff edf1bed4 eefec490
[    4.912955] be88  00000000 ee3edd80 edf1bf14 edf1bea0 c08ba618 c0008364 ee3edd80 ee3edd80
[    4.913596] bea8  00000002 c04d66bc 00000000 ee3edd80 00000010 ef3c8d00 eefec490 00000000
[    4.914207] bec8  ee3edd80 edf1bf14 edf1bf18 edf1bee8 c04b28d4 c04d66d8 60000013 ffffffff
[    4.914878] bee8  c04d66bc ef033400 ee3edd80 00000010 ef3c8d00 eefec490 00000000 ee3edd88
[    4.915550] bf08  edf1bf2c edf1bf18 c04b28d4 c04d66c8 ee3edd80 ef0a94b0 edf1bf64 edf1bf30
[    4.916191] bf28  c0148514 c04b288c 00000000 00000000 00000073 ee3edd80 00000000 eefee400
[    4.916862] bf48  ee3edd80 c000e2a8 edf1a000 00000000 edf1bf84 edf1bf68 c01441b0 c0148400
[    4.917564] 
[    4.917564] IP: 0xedf1be98:
[    4.917686] be98  c08ba618 c0008364 ee3edd80 ee3edd80 00000002 c04d66bc 00000000 ee3edd80
[    4.918327] beb8  00000010 ef3c8d00 eefec490 00000000 ee3edd80 edf1bf14 edf1bf18 edf1bee8
[    4.918998] bed8  c04b28d4 c04d66d8 60000013 ffffffff c04d66bc ef033400 ee3edd80 00000010
[    4.919639] bef8  ef3c8d00 eefec490 00000000 ee3edd88 edf1bf2c edf1bf18 c04b28d4 c04d66c8
[    4.920311] bf18  ee3edd80 ef0a94b0 edf1bf64 edf1bf30 c0148514 c04b288c 00000000 00000000
[    4.920982] bf38  00000073 ee3edd80 00000000 eefee400 ee3edd80 c000e2a8 edf1a000 00000000
[    4.921623] bf58  edf1bf84 edf1bf68 c01441b0 c0148400 00000000 00000003 eefee400 eefee440
[    4.922234] bf78  edf1bfa4 edf1bf88 c014427c c014413c 00011000 00000003 40000000 00000006
[    4.922905] 
[    4.922905] FP: 0xedf1be94:
[    4.923027] be94  edf1bea0 c08ba618 c0008364 ee3edd80 ee3edd80 00000002 c04d66bc 00000000
[    4.923668] beb4  ee3edd80 00000010 ef3c8d00 eefec490 00000000 ee3edd80 edf1bf14 edf1bf18
[    4.924339] bed4  edf1bee8 c04b28d4 c04d66d8 60000013 ffffffff c04d66bc ef033400 ee3edd80
[    4.924980] bef4  00000010 ef3c8d00 eefec490 00000000 ee3edd88 edf1bf2c edf1bf18 c04b28d4
[    4.925591] bf14  c04d66c8 ee3edd80 ef0a94b0 edf1bf64 edf1bf30 c0148514 c04b288c 00000000
[    4.926232] bf34  00000000 00000073 ee3edd80 00000000 eefee400 ee3edd80 c000e2a8 edf1a000
[    4.926842] bf54  00000000 edf1bf84 edf1bf68 c01441b0 c0148400 00000000 00000003 eefee400
[    4.927483] bf74  eefee440 edf1bfa4 edf1bf88 c014427c c014413c 00011000 00000003 40000000
[    4.928094] 
[    4.928094] R0: 0xee3edd00:
[    4.928277] dd00  00000000 00000000 ee34bd00 00000000 00000000 00000000 00000000 00000020
[    4.928887] dd20  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee530780 00000000
[    4.929558] dd40  ee3edd40 ee3edd40 ee3edd48 ee3edd48 ee670f38 00000000 00000000 00000000
[    4.930138] dd60  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    4.930810] dd80  ee3ed3c0 c387e194 eefec490 ef3c8d00 c092c7f8 00000000 00000002 00000000
[    4.931481] dda0  00020000 0000001d 00000000 00000000 00000000 00000000 00000000 00000000
[    4.932183] ddc0  00000000 00000000 ee34b900 00000000 00000000 00000000 00000000 00000000
[    4.932855] dde0  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee405600 00000000
[    4.933496] 
[    4.933496] R1: 0xee3edd00:
[    4.933679] dd00  00000000 00000000 ee34bd00 00000000 00000000 00000000 00000000 00000020
[    4.934350] dd20  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee530780 00000000
[    4.935022] dd40  ee3edd40 ee3edd40 ee3edd48 ee3edd48 ee670f38 00000000 00000000 00000000
[    4.935724] dd60  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    4.936395] dd80  ee3ed3c0 c387e194 eefec490 ef3c8d00 c092c7f8 00000000 00000002 00000000
[    4.937005] dda0  00020000 0000001d 00000000 00000000 00000000 00000000 00000000 00000000
[    4.937646] ddc0  00000000 00000000 ee34b900 00000000 00000000 00000000 00000000 00000000
[    4.938348] dde0  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee405600 00000000
[    4.939020] 
[    4.939020] R3: 0xc04d663c:
[    4.939142] 663c  e2455001 e7930006 ebf1a9be e594324c e7839006 e3750001 e2466004 1afffff6
[    4.939783] 665c  e594024c ebf1a9b7 e3a03000 e584324c e1a00008 e3e0700b eb0f8442 ea000008
[    4.940424] 667c  e2855001 eaffffff e5963000 e1550003 3affffd8 e5963000 e5843248 e1a00008
[    4.941065] 669c  eb0f8438 e1a00007 e89daff8 c0b6408b c0b63c39 c092def1 c0b63c50 c0b63c69
[    4.941736] 66bc  e1a0c00d e92ddff8 e24cb004 e52de004 e8bd4000 e590407c e1a0a000 e5945238
[    4.942408] 66dc  e3550000 1a000004 e59f0128 e3e07015 e59f1124 eb0f4d12 ea000044 e595041c
[    4.943018] 66fc  e2858e16 eb0014ae e2849fbf e1a06000 e1a00008 eb0f849f e1a00009 eb0f849d
[    4.943689] 671c  e5953174 e3530001 13a07000 1a000009 e1a00005 eb002052 e2507000 a3a06000
[    4.944330] 
[    4.944330] R5: 0xee3edd00:
[    4.944452] dd00  00000000 00000000 ee34bd00 00000000 00000000 00000000 00000000 00000020
[    4.945124] dd20  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee530780 00000000
[    4.945765] dd40  ee3edd40 ee3edd40 ee3edd48 ee3edd48 ee670f38 00000000 00000000 00000000
[    4.946375] dd60  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    4.947047] dd80  ee3ed3c0 c387e194 eefec490 ef3c8d00 c092c7f8 00000000 00000002 00000000
[    4.947718] dda0  00020000 0000001d 00000000 00000000 00000000 00000000 00000000 00000000
[    4.948298] ddc0  00000000 00000000 ee34b900 00000000 00000000 00000000 00000000 00000000
[    4.948908] dde0  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee405600 00000000
[    4.949580] 
[    4.949580] R7: 0xef3c8c80:
[    4.949702] 8c80  00000088 00000004 00000000 c38be320 ef221000 d9d3cd40 00000006 ef3c8ca4
[    4.950343] 8ca0  ef0a9338 65646976 ef00306f ef3c8ca8 ef3c8cb0 ef3c8cb0 ef3c8b60 ef3c8e10
[    4.951014] 8cc0  ef23d6f8 ef23d6f8 00000001 001e001e c08d5480 cf708000 00000000 00000000
[    4.951625] 8ce0  ef3c8ce0 ef3c8ce0 ef3c8c68 ef3c8d68 ef3c8cf0 ef3c8cf0 ef0a93e0 ef0a93e0
[    4.952235] 8d00  00000088 00000004 00000000 c38be5e0 ef221000 d9d3cdf0 00000006 ef3c8d24
[    4.952907] 8d20  ef0a94b0 65646976 0000316f c08d50f4 000200da c0dedc08 00000000 ef3c8d3c
[    4.953547] 8d40  ef3c8d3c 00000000 00000002 00150015 c08d5480 cf708000 00000000 00000000
[    4.954158] 8d60  ef3c8d60 ef3c8d60 ef3c8ce8 ef3c8de8 ef3c8d70 ef3c8d70 ef0a9558 ef0a9558
[    4.954829] 
[    4.954829] R8: 0xeefec410:
[    4.955012] c410  00000000 00000000 00000000 00000020 00000000 00000000 00007131 00000000
[    4.955623] c430  00000000 00000000 eedcc280 00000000 eefec440 eefec440 eefec448 eefec448
[    4.956264] c450  ee63d628 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    4.956935] c470  00000000 00000000 00000000 00000000 ee21f540 e2f21718 eec47c00 ee662780
[    4.957546] c490  ef221000 cf708000 00000020 c0d57fa8 00000001 eefc69ec eefc69ec eead126c
[    4.958217] c4b0  eec47c24 cf708084 e2fe10f4 eefde580 eefc6a00 eefc6640 eefec4c8 eefec4c8
[    4.958858] c4d0  eefec4d0 eefec4d0 eefec4d8 eefec4d8 eefec4e0 eefec4e0 00000000 e2f206c0
[    4.959529] c4f0  00000000 00000000 0000000f 00000000 00000000 00000000 00000000 00000000
[    4.960140] 
[    4.960140] R10: 0xee3edd00:
[    4.960292] dd00  00000000 00000000 ee34bd00 00000000 00000000 00000000 00000000 00000020
[    4.960903] dd20  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee530780 00000000
[    4.961544] dd40  ee3edd40 ee3edd40 ee3edd48 ee3edd48 ee670f38 00000000 00000000 00000000
[    4.962215] dd60  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    4.962856] dd80  ee3ed3c0 c387e194 eefec490 ef3c8d00 c092c7f8 00000000 00000002 00000000
[    4.963467] dda0  00020000 0000001d 00000000 00000000 00000000 00000000 00000000 00000000
[    4.964138] ddc0  00000000 00000000 ee34b900 00000000 00000000 00000000 00000000 00000000
[    4.964779] dde0  00000000 00000000 ffffffff ffffffff 00000000 00000000 ee405600 00000000
[    4.965389] Process v4l_id (pid: 556, stack limit = 0xedf1a2f0)
[    4.965450] Stack: (0xedf1bee8 to 0xedf1c000)
[    4.965542] bee0:                   c04d66bc ef033400 ee3edd80 00000010 ef3c8d00 eefec490
[    4.965634] bf00: 00000000 ee3edd88 edf1bf2c edf1bf18 c04b28d4 c04d66c8 ee3edd80 ef0a94b0
[    4.965756] bf20: edf1bf64 edf1bf30 c0148514 c04b288c 00000000 00000000 00000073 ee3edd80
[    4.965878] bf40: 00000000 eefee400 ee3edd80 c000e2a8 edf1a000 00000000 edf1bf84 edf1bf68
[    4.965969] bf60: c01441b0 c0148400 00000000 00000003 eefee400 eefee440 edf1bfa4 edf1bf88
[    4.966091] bf80: c014427c c014413c 00011000 00000003 40000000 00000006 00000000 edf1bfa8
[    4.966183] bfa0: c000e020 c01441c8 00011000 00000003 00000003 00000001 00000000 00000001
[    4.966274] bfc0: 00011000 00000003 40000000 00000006 00000000 00000000 4011b000 00000000
[    4.966336] bfe0: 00000000 be995c84 000085a1 402b698c 60000010 00000003 b01fc821 b01fcc21
[    4.966488] [<c04d66d8>] (msm_mctl_dev_close+0x1c/0x164) from [<c04b28d4>] (v4l2_release+0x54/0x74)
[    4.966641] [<c04b28d4>] (v4l2_release+0x54/0x74) from [<c0148514>] (fput+0x120/0x234)
[    4.966732] [<c0148514>] (fput+0x120/0x234) from [<c01441b0>] (filp_close+0x80/0x8c)
[    4.966854] [<c01441b0>] (filp_close+0x80/0x8c) from [<c014427c>] (sys_close+0xc0/0xf8)
[    4.966976] [<c014427c>] (sys_close+0xc0/0xf8) from [<c000e020>] (ret_fast_syscall+0x0/0x30)
[    4.967099] Code: e52de004 e8bd4000 e590407c e1a0a000 (e5945238) 
[    4.968564] ---[ end trace c1b524d510d4fd81 ]---
[    4.968686] Kernel panic - not syncing: Fatal exception
[    4.968747] CPU0: stopping
[    4.968838] [<c00154e4>] (unwind_backtrace+0x0/0xec) from [<c08a936c>] (dump_stack+0x20/0x24)
[    4.968960] [<c08a936c>] (dump_stack+0x20/0x24) from [<c00139a4>] (handle_IPI+0x110/0x1e4)
[    4.969082] [<c00139a4>] (handle_IPI+0x110/0x1e4) from [<c0008688>] (gic_handle_irq+0xb8/0xc4)
[    4.969204] [<c0008688>] (gic_handle_irq+0xb8/0xc4) from [<c08ba840>] (__irq_usr+0x40/0x60)
[    4.969265] Exception stack(0xee3e3fb0 to 0xee3e3ff8)
[    4.969388] 3fa0:                                     005e8d28 00000002 005e8c98 005e8444
[    4.969449] 3fc0: 005e9000 005e9000 beb35950 00000000 00000004 00000005 00000001 005e8208
[    4.969571] 3fe0: 00031db8 beb358b8 0001c583 0001c4dc 200f0030 ffffffff
[    4.969662] CPU3: stopping
[    4.969754] [<c00154e4>] (unwind_backtrace+0x0/0xec) from [<c08a936c>] (dump_stack+0x20/0x24)
[    4.969876] [<c08a936c>] (dump_stack+0x20/0x24) from [<c00139a4>] (handle_IPI+0x110/0x1e4)
[    4.969937] [<c00139a4>] (handle_IPI+0x110/0x1e4) from [<c0008688>] (gic_handle_irq+0xb8/0xc4)
[    4.970059] [<c0008688>] (gic_handle_irq+0xb8/0xc4) from [<c08ba840>] (__irq_usr+0x40/0x60)
[    4.970181] Exception stack(0xeecfbfb0 to 0xeecfbff8)
[    4.970242] bfa0:                                     01fe78a8 00025da8 00000007 00000007
[    4.970364] bfc0: 01fe77c0 01fe7888 bed660bc 00025da8 fffffffb 00000000 bed66558 bed66673
[    4.970456] bfe0: 40538010 bed66090 0001bc43 4050eb24 600f0010 ffffffff
[    4.970547] CPU1: stopping
[    4.970669] [<c00154e4>] (unwind_backtrace+0x0/0xec) from [<c08a936c>] (dump_stack+0x20/0x24)
[    4.970730] [<c08a936c>] (dump_stack+0x20/0x24) from [<c00139a4>] (handle_IPI+0x110/0x1e4)
[    4.970853] [<c00139a4>] (handle_IPI+0x110/0x1e4) from [<c0008688>] (gic_handle_irq+0xb8/0xc4)
[    4.970975] [<c0008688>] (gic_handle_irq+0xb8/0xc4) from [<c08ba680>] (__irq_svc+0x40/0x70)
[    4.971097] Exception stack(0xee449dc0 to 0xee449e08)
[    4.971158] 9dc0: ef4d4e4c 00000000 00000000 00000000 ee3ba300 ee449ed8 00000000 eeb4de00
[    4.971249] 9de0: 00000000 00000000 00000000 ee449e2c ee449df0 ee449e08 c015046c c0145824
[    4.971371] 9e00: 60000013 ffffffff
[    4.971432] [<c08ba680>] (__irq_svc+0x40/0x70) from [<c0145824>] (nameidata_to_filp+0x4c/0x74)
[    4.971555] [<c0145824>] (nameidata_to_filp+0x4c/0x74) from [<c0154adc>] (do_last+0x820/0x83c)
[    4.971646] [<c0154adc>] (do_last+0x820/0x83c) from [<c0154d00>] (path_openat+0xc8/0x388)
[    4.971768] [<c0154d00>] (path_openat+0xc8/0x388) from [<c01550e4>] (do_filp_open+0x3c/0x88)
[    4.971860] [<c01550e4>] (do_filp_open+0x3c/0x88) from [<c0145938>] (do_sys_open+0xec/0x178)
[    4.971982] [<c0145938>] (do_sys_open+0xec/0x178) from [<c01459f4>] (sys_open+0x30/0x34)
[    4.972073] [<c01459f4>] (sys_open+0x30/0x34) from [<c000e020>] (ret_fast_syscall+0x0/0x30)
[    4.972226] wcnss_8960: crash shutdown : 0