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The BIOS can leave TypeC HPD live\nstatus bits set on an XeLPDP TC port indicating a connected device, while\nTCSS (TypeC Subsystem) power has not been enabled. During driver probe,\nthis causes drm_WARN_ON to fire in xelpdp_tc_phy_get_hw_state() even\nthough the driver correctly handles this state afterwards.\nThe warning triggers failures in automated cold-boot/warm-boot stress test\nplans (cold-boot-loop-test, warm-boot-loop-test).\nError log:\ni915 0000:00:02.0: [drm] drm_WARN_ON((tc->mode == TC_PORT_DP_ALT || tc->mode == TC_PORT_LEGACY) && !xelpdp_tc_phy_tcss_power_is_enabled(tc))\nWARNING: CPU: 7 PID: 591 at drivers/gpu/drm/i915/display/intel_tc.c:1177 xelpdp_tc_phy_get_hw_state+0x145/0x150 [i915]\nCall Trace:\n intel_tc_port_init_mode+0x73/0x270 [i915]\n intel_tc_port_init+0x1e0/0x2a0 [i915]\n intel_ddi_init+0xa9a/0x1220 [i915]\n intel_setup_outputs+0x1f4/0xc20 [i915]\n intel_display_driver_probe_nogem+0x16f/0x270 [i915]\n i915_driver_probe+0x251/0x670 [i915]\n\n[Fix]\nConvert the drm_WARN_ON in xelpdp_tc_phy_get_hw_state() to a drm_dbg_kms()\nmessage. The stale HPD bits left by BIOS are a known handoff condition that\nthe driver already handles correctly via intel_tc_port_update_mode(); the\nWARN_ON is a false positive that need not be a warning.\nThis is consistent with the approach taken for the analogous AUX power check\nin commit 5830231e6547 (\"drm/i915/icl+/tc: Convert AUX powered WARN to a\ndebug message\"), which is already in the tree.\n\nhttps://lore.kernel.org/lkml/20260316093001.689992-1-acelan.kao@canonical.com/T/#u\n\n[Test Plan]\nBoot the system without a monitor connected and check dmesg:\n$ sudo dmesg | grep -i \"warn_on.*xelpdp\\|WARNING.*intel_tc\"\nWithout the patch: WARNING at intel_tc.c:1177 xelpdp_tc_phy_get_hw_state\nis present in dmesg on affected hardware.\nWith the patch: No WARNING or drm_WARN_ON in dmesg related to\nxelpdp_tc_phy_get_hw_state.\nTo stress test, run multiple cold/warm boot cycles:\n$ sudo reboot # repeat 10+ times, check dmesg each boot\n\n[Where problems could occur]\nIt may affect Intel XeLPDP TC port state detection in the i915 driver on\nMTL/ARL platforms.\nThe WARN_ON being converted was asserting that TCSS power must be enabled\nwhen the port mode is DP-alt or Legacy. By downgrading it to a debug\nmessage, a genuinely unexpected hardware state (not just a BIOS handoff\nartifact) could go unnoticed and silently result in incorrect TC port\nmode initialisation. This could manifest as a TC/USB4 port failing to\nenumerate connected devices or DisplayPort-alt mode not working on\naffected TC ports after boot.\nThe risk is limited to XeLPDP platforms (MTL, ARL) and only triggers\nduring the specific BIOS handoff scenario where HPD bits are stale.\n\nChia-Lin Kao (AceLan) (1):\n UBUNTU: SAUCE: drm/i915/xelpdp/tc: Convert TCSS power check WARN to a\n debug message\n\n drivers/gpu/drm/i915/display/intel_tc.c | 7 ++++---\n 1 file changed, 4 insertions(+), 3 deletions(-)"}