drm/i915/dg2: Do not explode on phy calibration error

When the PHY fails on calibration we were previously skipping the ddi
initialization. However the driver is not really prepared for that,
ultimately leading to a NULL pointer dereference:

[   75.748348] i915 0000:03:00.0: [drm:intel_modeset_init_nogem [i915]] SNPS PHY A failed to calibrate; output will not be used.
...
[   75.750336] i915 0000:03:00.0: [drm:intel_modeset_setup_hw_state [i915]] [CRTC:80:pipe A] hw state readout: enabled
...

( no DDI A/PHY A )
[   75.753080] i915 0000:03:00.0: [drm:intel_modeset_setup_hw_state [i915]] [ENCODER:235:DDI B/PHY B] hw state readout: disabled, pipe A
[   75.753164] i915 0000:03:00.0: [drm:intel_modeset_setup_hw_state [i915]] [ENCODER:245:DDI C/PHY C] hw state readout: disabled, pipe A
...
[   75.754425] i915 0000:03:00.0: [drm] *ERROR* crtc 80: Can't calculate constants, dotclock = 0!
[   75.765558] i915 0000:03:00.0: drm_WARN_ON_ONCE(drm_drv_uses_atomic_modeset(dev))
[   75.765569] WARNING: CPU: 5 PID: 1759 at drivers/gpu/drm/drm_vblank.c:728 drm_crtc_vblank_helper_get_vblank_timestamp_internal+0x347/0x360
...
[   75.781230] BUG: kernel NULL pointer dereference, address: 000000000000007c
[   75.788198] #PF: supervisor read access in kernel mode
[   75.793347] #PF: error_code(0x0000) - not-present page
[   75.798480] PGD 0 P4D 0
[   75.801019] Oops: 0000 [#1] PREEMPT SMP NOPTI
[   75.805377] CPU: 5 PID: 1759 Comm: modprobe Tainted: G        W         5.18.0-rc1-demarchi+ #199
[   75.827613] RIP: 0010:icl_aux_power_well_disable+0x3b/0x200 [i915]
[   75.833890] Code: 83 ec 30 65 48 8b 04 25 28 00 00 00 48 89 44 24 28 48 8b 06 0f b6 70 1c f6 40 20 04 8d 56 fa 0f 45 f2 e8 88 bd ff ff 48 89 ef <8b> 70 7c e8 ed 67 ff ff 48 89 ef 89 c6 e8 73 67 ff ff 84 c0 75 0a
[   75.852629] RSP: 0018:ffffc90003a7fb30 EFLAGS: 00010246
[   75.857852] RAX: 0000000000000000 RBX: ffff8881145e8f10 RCX: 0000000000000000
[   75.864978] RDX: ffff888115220840 RSI: 0000000000000000 RDI: ffff888115220000
[   75.872106] RBP: ffff888115220000 R08: ffff88888effffe8 R09: 00000000fffdffff
[   75.879234] R10: ffff88888e200000 R11: ffff88888ed00000 R12: ffff8881145e8f10
[   75.886363] R13: 0000000000000001 R14: ffff888115223240 R15: 0000000000000000
[   75.893490] FS:  00007ff6e753a740(0000) GS:ffff88888f680000(0000) knlGS:0000000000000000
[   75.901573] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   75.907313] CR2: 000000000000007c CR3: 00000001216a6001 CR4: 0000000000770ee0
[   75.914446] PKRU: 55555554
[   75.917153] Call Trace:
[   75.919603]  <TASK>
[   75.921709]  intel_power_domains_sanitize_state+0x88/0xb0 [i915]
[   75.927814]  intel_modeset_init_nogem+0x317/0xef0 [i915]
[   75.933205]  i915_driver_probe+0x5f6/0xdf0 [i915]
[   75.937976]  i915_pci_probe+0x51/0x1d0 [i915]

We skip the initialization of PHY A, but later we try to find out what
is the phy for that power well and dereference dig_port, which is NULL.

Failing the PHY calibration could be left as a warning or error, like it
was before commit b4eb76d82a ("drm/i915/dg2: Skip output init on PHY
calibration failure"). However that often fails for outputs not being
used, which would make the warning/error appear on systems that have no
visible issues. Anyway, there is still a need to fix those failures,
but that is left for later.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220410061537.4187383-1-lucas.demarchi@intel.com

drivers/gpu/drm/i915/display/intel_ddi.c

@@ -4300,9 +4300,8 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
 	if (intel_phy_is_snps(dev_priv, phy) &&
 	    dev_priv->snps_phy_failed_calibration & BIT(phy)) {
 		drm_dbg_kms(&dev_priv->drm,
-			    "SNPS PHY %c failed to calibrate; output will not be used.\n",
+			    "SNPS PHY %c failed to calibrate, proceeding anyway\n",
 			    phy_name(phy));
-		return;
 	}
 
 	dig_port = kzalloc(sizeof(*dig_port), GFP_KERNEL);