During boot, I get this kernel warning:

WARNING: CPU: 0 PID: 19001 at kernel/dma/debug.c:1301 debug_dma_map_sg+0x284/0x3dc
etnaviv etnaviv: DMA-API: mapping sg segment longer than device claims to support [len=3145728] [max=65536]
Modules linked in: ip6t_REJECT nf_reject_ipv6 ip6t_rpfilter xt_tcpudp ipt_REJECT nf_reject_ipv4 xt_conntrack ip_set nfnetlink ebtable_broute ebtable_nat ip6table_raw ip6table_nat nf_nat_ipv6 ip6table_mangle iptable_raw iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv4 nf_defrag_ipv6 libcrc32c iptable_mangle ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter caam_jr error snd_soc_imx_spdif imx_thermal snd_soc_imx_audmux nvmem_imx_ocotp snd_soc_sgtl5000
caam imx_sdma virt_dma coda rc_cec v4l2_mem2mem snd_soc_fsl_ssi snd_soc_fsl_spdif imx_vdoa imx_pcm_dma videobuf2_dma_contig etnaviv dw_hdmi_cec gpu_sched dw_hdmi_ahb_audio imx6q_cpufreq nfsd sch_fq_codel ip_tables x_tables
CPU: 0 PID: 19001 Comm: Xorg Not tainted 4.20.0+ #307
Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[<c0019658>] (unwind_backtrace) from [<c001489c>] (show_stack+0x10/0x14)
[<c001489c>] (show_stack) from [<c07fb420>] (dump_stack+0x9c/0xd4)
[<c07fb420>] (dump_stack) from [<c00312dc>] (__warn+0xf8/0x124)
[<c00312dc>] (__warn) from [<c00313d0>] (warn_slowpath_fmt+0x38/0x48)
[<c00313d0>] (warn_slowpath_fmt) from [<c00b14e8>] (debug_dma_map_sg+0x284/0x3dc)
[<c00b14e8>] (debug_dma_map_sg) from [<c046eb40>] (drm_gem_map_dma_buf+0xc4/0x13c)
[<c046eb40>] (drm_gem_map_dma_buf) from [<c04c3314>] (dma_buf_map_attachment+0x38/0x5c)
[<c04c3314>] (dma_buf_map_attachment) from [<c046e728>] (drm_gem_prime_import_dev+0x74/0x104)
[<c046e728>] (drm_gem_prime_import_dev) from [<c046e5bc>] (drm_gem_prime_fd_to_handle+0x84/0x17c)
[<c046e5bc>] (drm_gem_prime_fd_to_handle) from [<c046edd0>] (drm_prime_fd_to_handle_ioctl+0x38/0x4c)
[<c046edd0>] (drm_prime_fd_to_handle_ioctl) from [<c0460efc>] (drm_ioctl_kernel+0x90/0xc8)
[<c0460efc>] (drm_ioctl_kernel) from [<c0461114>] (drm_ioctl+0x1e0/0x3b0)
[<c0461114>] (drm_ioctl) from [<c01cae20>] (do_vfs_ioctl+0x90/0xa48)
[<c01cae20>] (do_vfs_ioctl) from [<c01cb80c>] (ksys_ioctl+0x34/0x60)
[<c01cb80c>] (ksys_ioctl) from [<c0009000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xd81a9fa8 to 0xd81a9ff0)
9fa0:                   b6c69c88 bec613f8 00000009 c00c642e bec613f8 b86c4600
9fc0: b6c69c88 bec613f8 c00c642e 00000036 012762e0 01276348 00000300 012d91f8
9fe0: b6989f18 bec613dc b697185c b667be5c
irq event stamp: 47905
hardirqs last  enabled at (47913): [<c0098824>] console_unlock+0x46c/0x680
hardirqs last disabled at (47922): [<c0098470>] console_unlock+0xb8/0x680
softirqs last  enabled at (47754): [<c000a484>] __do_softirq+0x344/0x540
softirqs last disabled at (47701): [<c0038700>] irq_exit+0x124/0x144
---[ end trace af477747acbcc642 ]---

The reason is the contiguous buffer exceeds the default maximum segment
size of 64K as specified by dma_get_max_seg_size() in
linux/dma-mapping.h.  Fix this by providing our own segment size, which
is set to 2GiB to cover the window found in MMUv1 GPUs.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>