8415ab565d
According to the kerneldoc[0], should do fbdev setup before calling drm_kms_helper_poll_init(), otherwise, Kms hotplug event may race into fbdev helper initial, and fb_helper->dev may be NULL pointer, that would cause the bug: [ 0.735411] [00000200] *pgd=00000000f6ffe003, *pud=00000000f6ffe003, *pmd=0000000000000000 [ 0.736156] Internal error: Oops: 96000005 [#1] PREEMPT SMP [ 0.736648] Modules linked in: [ 0.736930] CPU: 2 PID: 20 Comm: kworker/2:0 Not tainted 4.4.41 #20 [ 0.737480] Hardware name: Rockchip RK3399 Board rev2 (BOX) (DT) [ 0.738020] Workqueue: events cdn_dp_pd_event_work [ 0.738447] task: ffffffc0f21f3100 ti: ffffffc0f2218000 task.ti: ffffffc0f2218000 [ 0.739109] PC is at mutex_lock+0x14/0x44 [ 0.739469] LR is at drm_fb_helper_hotplug_event+0x30/0x114 [ 0.756253] [<ffffff8008a344f4>] mutex_lock+0x14/0x44 [ 0.756260] [<ffffff8008445708>] drm_fb_helper_hotplug_event+0x30/0x114 [ 0.756271] [<ffffff8008473c84>] rockchip_drm_output_poll_changed+0x18/0x20 [ 0.756280] [<ffffff8008439fcc>] drm_kms_helper_hotplug_event+0x28/0x34 [ 0.756286] [<ffffff800846c444>] cdn_dp_pd_event_work+0x394/0x3c4 [ 0.756295] [<ffffff80080b2b38>] process_one_work+0x218/0x3e0 [ 0.756302] [<ffffff80080b3538>] worker_thread+0x2e8/0x404 [ 0.756308] [<ffffff80080b7e70>] kthread+0xe8/0xf0 [ 0.756316] [<ffffff8008082690>] ret_from_fork+0x10/0x40 [0]: https://01.org/linuxgraphics/gfx-docs/drm/gpu/drm-kms-helpers.html Signed-off-by: Mark Yao <mark.yao@rock-chips.com> Reviewed-by: Sandy huang <sandy.huang@rock-chips.com> Link: https://patchwork.freedesktop.org/patch/msgid/1501575103-20136-1-git-send-email-mark.yao@rock-chips.com
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.