I occasionally get this:

[   11.708548] ------------[ cut here ]------------
[   11.708598] i915 0000:00:02.0: DMA-API: mapping sg segment longer than device claims to support [len=2883584] [max=65536]
[   11.708612] WARNING: CPU: 0 PID: 408 at kernel/dma/debug.c:1301 debug_dma_map_sg+0x229/0x350
[   11.708615] Modules linked in: i915 i2c_algo_bit drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel ax88179_178a usbnet serio_raw mii i2c_hid i2c_core video
[   11.708662] CPU: 0 PID: 408 Comm: plymouthd Not tainted 4.19.0-rc8-drm+ #3
[   11.708665] Hardware name: HP HP EliteBook Folio G1/8170, BIOS N91 Ver. 01.10 07/19/2016
[   11.708671] RIP: 0010:debug_dma_map_sg+0x229/0x350
[   11.708675] Code: 4d 54 00 8b 4c 24 08 48 8b 54 24 10 4c 8b 5c 24 18 44 8b 44 24 24 48 89 c6 48 c7 c7 10 67 0d ac 4c 89 5c 24 08 e8 9f 79 f6 ff <0f> 0b 4c 8b 5c 24 08 8b 15 f2 87 63 01 85 d2 0f 85 21 fe ff ff 8b
[   11.708678] RSP: 0018:ffffae73817939d8 EFLAGS: 00010286
[   11.708684] RAX: 0000000000000000 RBX: ffff9f018715b320 RCX: 0000000000000006
[   11.708687] RDX: 0000000000000007 RSI: ffff9f01903b0d78 RDI: ffff9f01a0dd6be0
[   11.708690] RBP: ffff9f019e7bb0a8 R08: 0000000c56c24271 R09: 0000000000000000
[   11.708693] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
[   11.708696] R13: 0000000000000004 R14: 00000000ffffffff R15: ffff9f019f027540
[   11.708700] FS:  00007f7f5d49f240(0000) GS:ffff9f01a0c00000(0000) knlGS:0000000000000000
[   11.708703] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   11.708705] CR2: 00007f54a5937b10 CR3: 000000028e63e001 CR4: 00000000003606f0
[   11.708707] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   11.708709] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   11.708711] Call Trace:
[   11.708752]  i915_gem_gtt_prepare_pages+0x74/0xd0 [i915]
[   11.708780]  i915_gem_object_get_pages_gtt+0x22e/0x640 [i915]
[   11.708812]  __i915_gem_object_get_pages+0x54/0x60 [i915]
[   11.708842]  intel_prepare_plane_fb+0x172/0x420 [i915]
[   11.708847]  ? is_module_address+0x11/0x20
[   11.708860]  drm_atomic_helper_prepare_planes+0x4f/0xd0 [drm_kms_helper]
[   11.708890]  intel_atomic_commit+0xab/0x310 [i915]
[   11.708901]  drm_atomic_helper_set_config+0x75/0x80 [drm_kms_helper]
[   11.708918]  drm_mode_setcrtc+0x1aa/0x6b0 [drm]
[   11.708949]  ? drm_mode_getcrtc+0x180/0x180 [drm]
[   11.708960]  drm_ioctl_kernel+0xa9/0xf0 [drm]
[   11.708975]  drm_ioctl+0x1fc/0x390 [drm]
[   11.708988]  ? drm_mode_getcrtc+0x180/0x180 [drm]
[   11.709000]  ? selinux_file_ioctl+0x171/0x210
[   11.709011]  do_vfs_ioctl+0xa5/0x6e0
[   11.709021]  ksys_ioctl+0x60/0x90
[   11.709027]  __x64_sys_ioctl+0x16/0x20
[   11.709031]  do_syscall_64+0x60/0x1f0
[   11.709035]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   11.709038] RIP: 0033:0x7f7f5c1bec57
[   11.709041] Code: 00 00 90 48 8b 05 49 82 2c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 19 82 2c 00 f7 d8 64 89 01 48
[   11.709043] RSP: 002b:00007ffce13d3f68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   11.709047] RAX: ffffffffffffffda RBX: 00007ffce13d3fa0 RCX: 00007f7f5c1bec57
[   11.709049] RDX: 00007ffce13d3fa0 RSI: 00000000c06864a2 RDI: 000000000000000a
[   11.709051] RBP: 00007ffce13d3fa0 R08: 0000000000000000 R09: 0000561854e244a0
[   11.709053] R10: 0000561854e242b0 R11: 0000000000000246 R12: 00000000c06864a2
[   11.709055] R13: 000000000000000a R14: 0000561854e242b0 R15: 0000000000000001
[   11.709068] irq event stamp: 142296
[   11.709077] hardirqs last  enabled at (142295): [<ffffffffab136c6d>] console_unlock+0x45d/0x600
[   11.709080] hardirqs last disabled at (142296): [<ffffffffab003828>] trace_hardirqs_off_thunk+0x1a/0x1c
[   11.709084] softirqs last  enabled at (142284): [<ffffffffabc00342>] __do_softirq+0x342/0x437
[   11.709087] softirqs last disabled at (142275): [<ffffffffab0c1e20>] irq_exit+0x110/0x120
[   11.709091] WARNING: CPU: 0 PID: 408 at kernel/dma/debug.c:1301 debug_dma_map_sg+0x229/0x350
[   11.709093] ---[ end trace d01531b8bf40edd1 ]---



If I weren't running a recent kernel right now (commit 90b59df999a13a6405f8d7ece08a69120a9b361a from drm-tip) I probably wouldn't bother reporting it :-)