Repeated kernel DRM error messages and very slow boot on Dell Vostro 1400 Laptop

I performed a fresh install of Ubuntu 18.04.3 ina Dell Laptop Vostro 1400 with an intel core 2 duo 9500T cpu.
Both during the boot from the USB installation key and during every subsequent boot after installation, the boot is very slow despite the SSD (with Linux mint 18.3 the system took 10-12 seconds to boot).
A dmesg command shows a long list of repeated error messages with sections to cut for a bug report.
I report one of these sections here:

[ 279.043445] ------------[ cut here ]------------
[ 279.043451] vblank wait timed out on crtc 1
[ 279.043586] WARNING: CPU: 0 PID: 1183 at /build/linux-hwe-lnnijC/linux-hwe-5.0.0/drivers/gpu/drm/drm_vblank.c:1084 drm_wait_one_vblank+0x17c/0x190 [drm]
[ 279.043589] Modules linked in: ccm snd_hda_codec_hdmi gpio_ich snd_hda_codec_idt snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep i915 snd_pcm dell_laptop ledtrig_audio dell_smm_hwmon arc4 snd_seq_midi kvmgt coretemp snd_seq_midi_event kvm_intel vfio_mdev mdev vfio_iommu_type1 snd_rawmidi vfio iwl3945 iwlegacy kvm uvcvideo dell_wmi irqbypass videobuf2_vmalloc mac80211 videobuf2_memops dell_smbios dcdbas wmi_bmof input_leds snd_seq serio_raw sparse_keymap dell_wmi_descriptor drm_kms_helper videobuf2_v4l2 videobuf2_common r852 videodev drm sm_common snd_seq_device cfg80211 media snd_timer nand nand_ecc i2c_algo_bit nand_bch bch r592 lpc_ich mtd fb_sys_fops memstick syscopyarea snd sysfillrect sysimgblt soundcore joydev mac_hid sch_fq_codel parport_pc ppdev lp parport ip_tables x_tables autofs4 sdhci_pci ahci psmouse cqhci libahci pata_acpi sdhci firewire_ohci firewire_core tg3 crc_itu_t wmi video
[ 279.043692] CPU: 0 PID: 1183 Comm: Xorg Tainted: G W OE 5.0.0-27-generic #28~18.04.1-Ubuntu
[ 279.043695] Hardware name: Dell Inc. Vostro 1400 /0TT347, BIOS A09 07/10/2008
[ 279.043740] RIP: 0010:drm_wait_one_vblank+0x17c/0x190 [drm]
[ 279.043746] Code: ff e8 a8 3a 84 fc 48 8d 75 a8 4c 89 ff e8 fc 0e 89 fc 45 85 ed 0f 85 04 ff ff ff 44 89 e6 48 c7 c7 c0 78 67 c0 e8 e4 37 84 fc <0f> 0b e9 ee fe ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 66 66
[ 279.043749] RSP: 0018:ffffb89b4130f910 EFLAGS: 00010286
[ 279.043754] RAX: 0000000000000000 RBX: ffff93ba595e0000 RCX: 0000000000000006
[ 279.043757] RDX: 0000000000000007 RSI: 0000000000000082 RDI: ffff93ba5ba16440
[ 279.043760] RBP: ffffb89b4130f968 R08: 00000000000004ff R09: 0000000000000004
[ 279.043763] R10: ffffb89b40a5fd68 R11: 0000000000000001 R12: 0000000000000001
[ 279.043767] R13: 0000000000000000 R14: 000000000f000794 R15: ffff93ba5a929978
[ 279.043771] FS: 00007f0afd553a80(0000) GS:ffff93ba5ba00000(0000) knlGS:0000000000000000
[ 279.043775] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 279.043778] CR2: 00007fd2c27eeea0 CR3: 00000000cc59e000 CR4: 00000000000006f0
[ 279.043781] Call Trace:
[ 279.043799] ? wait_woken+0x80/0x80
[ 279.043933] intel_get_load_detect_pipe+0x40b/0x420 [i915]
[ 279.044035] intel_tv_detect+0x140/0x4d0 [i915]
[ 279.044046] ? __ww_mutex_lock_slowpath+0x16/0x20
[ 279.044075] drm_helper_probe_detect+0x50/0x90 [drm_kms_helper]
[ 279.044096] ? drm_helper_probe_detect+0x50/0x90 [drm_kms_helper]
[ 279.044118] drm_helper_probe_single_connector_modes+0xe0/0x740 [drm_kms_helper]
[ 279.044173] drm_mode_getconnector+0x22d/0x500 [drm]
[ 279.044223] ? drm_connector_property_set_ioctl+0x60/0x60 [drm]
[ 279.044261] drm_ioctl_kernel+0xae/0xf0 [drm]
[ 279.044299] drm_ioctl+0x389/0x450 [drm]
[ 279.044346] ? drm_connector_property_set_ioctl+0x60/0x60 [drm]
[ 279.044354] ? nand_bch_init+0x2f7/0xe50 [nand_bch]
[ 279.044363] ? __fpu__restore_sig+0x78/0x4a0
[ 279.044370] do_vfs_ioctl+0xa9/0x640
[ 279.044378] ? recalc_sigpending+0x1b/0x50
[ 279.044386] ? _copy_from_user+0x3e/0x60
[ 279.044390] ksys_ioctl+0x75/0x80
[ 279.044396] __x64_sys_ioctl+0x1a/0x20
[ 279.044403] do_syscall_64+0x5a/0x120
[ 279.044409] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 279.044414] RIP: 0033:0x7f0afa7325d7
[ 279.044419] Code: b3 66 90 48 8b 05 b1 48 2d 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 81 48 2d 00 f7 d8 64 89 01 48
[ 279.044423] RSP: 002b:00007ffc10edf488 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 279.044428] RAX: ffffffffffffffda RBX: 0000562904833530 RCX: 00007f0afa7325d7
[ 279.044431] RDX: 00007ffc10edf4c0 RSI: 00000000c05064a7 RDI: 000000000000000c
[ 279.044434] RBP: 00007ffc10edf4c0 R08: 0000000000000000 R09: 0000000000000000
[ 279.044438] R10: 0000000000000000 R11: 0000000000000246 R12: 00000000c05064a7
[ 279.044441] R13: 000000000000000c R14: 000000000000000c R15: 00007ffc10edf4c0
[ 279.044447] ---[ end trace 88bff9e3faf015bb ]---
[ 289.180656] [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [CRTC:43:pipe B] flip_done timed out
[ 299.420609] [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [CONNECTOR:53:SVIDEO-1] flip_done timed out
[ 302.026400] rfkill: input handler disabled

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-5.0.0-27-generic 5.0.0-27.28~18.04.1
ProcVersionSignature: Ubuntu 5.0.0-27.28~18.04.1-generic 5.0.21
Uname: Linux 5.0.0-27-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Sep 11 13:36:03 2019
InstallationDate: Installed on 2019-09-10 (0 days ago)
InstallationMedia: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
SourcePackage: linux-signed-hwe
UpgradeStatus: No upgrade log present (probably fresh install)