drm/vblank: Fix for drivers that do not drm_vblank_init()

This should fix a crash that was reported on ast (and possibly other
drivers which do not initialize vblank).

   fbcon: Taking over console
   Unable to handle kernel NULL pointer dereference at virtual address 0000000000000074
   Mem abort info:
     ESR = 0x0000000096000004
     EC = 0x25: DABT (current EL), IL = 32 bits
     SET = 0, FnV = 0
     EA = 0, S1PTW = 0
     FSC = 0x04: level 0 translation fault
   Data abort info:
     ISV = 0, ISS = 0x00000004
     CM = 0, WnR = 0
   user pgtable: 4k pages, 48-bit VAs, pgdp=0000080009d16000
   [0000000000000074] pgd=0000000000000000, p4d=0000000000000000
   Internal error: Oops: 0000000096000004 [#1] SMP
   Modules linked in: ip6table_nat tun nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables nfnetlink qrtr sunrpc binfmt_misc vfat fat xfs snd_usb_audio snd_hwdep snd_usbmidi_lib snd_seq snd_pcm snd_rawmidi snd_timer snd_seq_device snd soundcore joydev mc ipmi_ssif ipmi_devintf ipmi_msghandler arm_spe_pmu arm_cmn arm_dsu_pmu arm_dmc620_pmu cppc_cpufreq loop zram crct10dif_ce polyval_ce nvme polyval_generic ghash_ce sbsa_gwdt igb nvme_core ast nvme_common i2c_algo_bit xgene_hwmon gpio_dwapb scsi_dh_rdac scsi_dh_emc scsi_dh_alua ip6_tables ip_tables dm_multipath fuse
   CPU: 12 PID: 469 Comm: kworker/12:1 Not tainted 6.3.0-rc2-00008-gd39e48ca #1
   Hardware name: ADLINK AVA Developer Platform/AVA Developer Platform, BIOS TianoCore 2.04.100.07 (SYS: 2.06.20220308) 09/08/2022
   Workqueue: events fbcon_register_existing_fbs
   pstate: 20400009 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
   pc : drm_crtc_next_vblank_start+0x2c/0x98
   lr : drm_atomic_helper_wait_for_fences+0x90/0x240
   sp : ffff80000d583960
   x29: ffff80000d583960 x28: ffff07ff8fc187b0 x27: 0000000000000000
   x26: ffff07ff99c08c00 x25: 0000000000000038 x24: ffff07ff99c0c000
   x23: 0000000000000001 x22: 0000000000000038 x21: 0000000000000000
   x20: ffff07ff9640a280 x19: 0000000000000000 x18: ffffffffffffffff
   x17: 0000000000000000 x16: ffffb24d2eece1c0 x15: 0000003038303178
   x14: 3032393100000048 x13: 0000000000000000 x12: 0000000000000000
   x11: 0000000000000000 x10: 0000000000000000 x9 : ffffb24d2eeeaca0
   x8 : ffff80000d583628 x7 : 0000080077783000 x6 : 0000000000000000
   x5 : ffff80000d584000 x4 : ffff07ff99c0c000 x3 : 0000000000000130
   x2 : 0000000000000000 x1 : ffff80000d5839c0 x0 : ffff07ff99c0cc08
   Call trace:
    drm_crtc_next_vblank_start+0x2c/0x98
    drm_atomic_helper_wait_for_fences+0x90/0x240
    drm_atomic_helper_commit+0xb0/0x188
    drm_atomic_commit+0xb0/0xf0
    drm_client_modeset_commit_atomic+0x218/0x280
    drm_client_modeset_commit_locked+0x64/0x1a0
    drm_client_modeset_commit+0x38/0x68
    __drm_fb_helper_restore_fbdev_mode_unlocked+0xb0/0xf8
    drm_fb_helper_set_par+0x44/0x88
    fbcon_init+0x1e0/0x4a8
    visual_init+0xbc/0x118
    do_bind_con_driver.isra.0+0x194/0x3a0
    do_take_over_console+0x50/0x70
    do_fbcon_takeover+0x74/0xf8
    do_fb_registered+0x13c/0x158
    fbcon_register_existing_fbs+0x78/0xc0
    process_one_work+0x1ec/0x478
    worker_thread+0x74/0x418
    kthread+0xec/0x100
    ret_from_fork+0x10/0x20
   Code: f9400004 b9409013 f940a082 9ba30a73 (b9407662)
   ---[ end trace 0000000000000000 ]---

v2: Use drm_dev_has_vblank()
Reported-by: Nathan Chancellor <nathan@kernel.org>
Fixes: d39e48ca ("drm/atomic-helper: Set fence deadline for vblank")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20230403160314.1210533-1-robdclark@gmail.com

drivers/gpu/drm/drm_vblank.c

@@ -996,10 +996,16 @@ EXPORT_SYMBOL(drm_crtc_vblank_count_and_time);
 int drm_crtc_next_vblank_start(struct drm_crtc *crtc, ktime_t *vblanktime)
 {
 	unsigned int pipe = drm_crtc_index(crtc);
-	struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
-	struct drm_display_mode *mode = &vblank->hwmode;
+	struct drm_vblank_crtc *vblank;
+	struct drm_display_mode *mode;
 	u64 vblank_start;
 
+	if (!drm_dev_has_vblank(crtc->dev))
+		return -EINVAL;
+
+	vblank = &crtc->dev->vblank[pipe];
+	mode = &vblank->hwmode;
+
 	if (!vblank->framedur_ns || !vblank->linedur_ns)
 		return -EINVAL;