[Intel-gfx] [PATCH] drm/i915/dg2: Do not explode on phy calibration error

[Lucas De Marchi]

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 b4eb76d82a0e ("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 at intel.com>
---
 drivers/gpu/drm/i915/display/intel_ddi.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
index cec578efc4bd..027cc4cc38d9 100644
--- a/drivers/gpu/drm/i915/display/intel_ddi.c
+++ b/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);
-- 
2.35.1