Two Lenovo ThinkPads, old T420s (2011), newer X1 Carbon 5th gen (2017): i915 working fine on both up to 5.14, but blank screens booting 5.15-rc1, kernel crashed in some way. I wanted to say what i915 generations these are, but don't know where to look - I don't see it in dmesg, even when DRM_I915_DEBUG enabled. Possibly relevant: builtin kernels, CONFIG_MODULES off, no initrd. On the older laptop: First bisection showed first bad commit 41e5c17ebfc2 "drm/i915/guc/slpc: Sysfs hooks for SLPC" But reverting that still crashed boot with blank screen (and reverting the two related commits after it made no difference). Second bisection, starting from 5.15-rc1 bad and 41e5c17ebfc2 "good", but patching it out each time before building, showed first bad commit 3ffe82d701a4 "drm/i915/xehp: handle new steering options" That one did not revert cleanly from 5.15-rc1, but reverting 927dfdd09d8c "drm/i915/dg2: Add SQIDI steering" then 1705f22c86fb "drm/i915/dg2: Update steering tables" then 768fe28dd3dc "drm/i915/xehpsdv: Define steering tables" then 3ffe82d701a4 "drm/i915/xehp: handle new steering options" worked (there was one very easy fixup needed somewhere). And 5.15-rc1 with those five reversions boots and runs fine... on that older laptop. But reverting those from the kernel on the newer laptop did not help at all, still booting with blank screen (or no more lines shown after the switch from VGA). Put them back. On the newer laptop, bisection showed first bad commit 62eaf0ae217d "drm/i915/guc: Support request cancellation" And 5.15-rc1 with that reverted boots and runs fine on the newer. I am hoping that there will be some i915 fixups to come in a later rc! May be nothing more than uninitialized variables or NULL pointers. You'll probably want more info from me: please ask, but I'm slow. Thanks, Hugh
