Dear All, Yesterday the "drm: Provide client setup helper and convert drivers" patchset [1] landed in linux-next. In my tests I found that it causes kernel NULL pointer dereference on ARM/ARM64 based Raspberry Pi4B boards. It turned out that the conversion of the VC4 DRM driver is a bit incomplete, so I've decided to provide the needed fix. While developping it I've found that a small fix to generic drm/fbdev-helper helps to avoid NULL pointer dereference in the future in case of similar problems. Those patches fixes the following problem observed on Raspberry Pi4B boards: 8<--- cut here --- Unable to handle kernel NULL pointer dereference at virtual address 00000020 when write [00000020] *pgd=00000000 Internal error: Oops: 805 [#1] SMP ARM Modules linked in: aes_arm aes_generic cmac brcmfmac_wcc brcmfmac brcmutil sha256_generic libsha256 sha256_arm cfg80211 hci_uart btbcm crc32_arm_ce raspberrypi_hwmon bluetooth ecdh_generic vc4 ecc libaes snd_soc_hdmi_codec snd_soc_core ac97_bus snd_pcm_dmaengine snd_pcm v3d bcm2711_thermal snd_timer genet drm_shmem_helper snd gpu_sched soundcore drm_dma_helper CPU: 1 UID: 0 PID: 21 Comm: kworker/1:0 Not tainted 6.12.0-rc1-next-20241002 #15363 Hardware name: BCM2711 Workqueue: events output_poll_execute PC is at __drm_fb_helper_initial_config_and_unlock+0x30c/0x518 LR is at __drm_fb_helper_initial_config_and_unlock+0x26c/0x518 pc : [<c0aec770>] lr : [<c0aec6d0>] psr: 60000013 ... Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5383d Table: 04ef006a DAC: 00000051 ... Register r12 information: slab task_struct start c213c400 pointer offset 0 size 2176 Process kworker/1:0 (pid: 21, stack limit = 0x98a73703) Stack: (0xf0879e28 to 0xf087a000) ... Call trace: __drm_fb_helper_initial_config_and_unlock from drm_client_dev_hotplug+0xac/0x104 drm_client_dev_hotplug from output_poll_execute+0x298/0x2a0 output_poll_execute from process_one_work+0x178/0x3c0 process_one_work from worker_thread+0x270/0x42c worker_thread from kthread+0xe0/0xfc kthread from ret_from_fork+0x14/0x28 Exception stack(0xf0879fb0 to 0xf0879ff8) 9fa0: 00000000 00000000 00000000 00000000 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 Code: e30a3724 e5942038 e34c3186 e8b30003 (e5820020) ---[ end trace 0000000000000000 ]--- [1] https://patchwork.freedesktop.org/series/137389/ Best regards Marek Szyprowski, PhD Samsung R&D Institute Poland Patch summary: Marek Szyprowski (2): drm/fbdev-helper: fail if driver provides no fbdev/fb probe functions drm/vc4: Provides DRM_FBDEV_DMA_DRIVER_OPS also for vc5_drm_driver drivers/gpu/drm/drm_fb_helper.c | 3 +++ drivers/gpu/drm/vc4/vc4_drv.c | 1 + 2 files changed, 4 insertions(+) -- 2.34.1
