drm: Bogus WARN() in drm_atomic_helper_update_legacy_modeset_state() ?

[Mark yao]

On 2015年11月10日 23:01, Liviu Dudau wrote:
> Hello,
>
> When booting my Juno board with the HDLCD driver that I have converted to
> atomic operations I'm getting the following warning:
>
> ------------[ cut here ]------------
> WARNING: at /work/repositories/kernel/drivers/gpu/drm/drm_atomic_helper.c:674
> Modules linked in: hdlcd(+) clk_scpi
>                  
> CPU: 3 PID: 1375 Comm: systemd-udevd Not tainted 4.3.0-next-20151109+ #5
> Hardware name: ARM Juno development board (r0) (DT)
> task: ffffffc974888b00 ti: ffffffc9755dc000 task.ti: ffffffc9755dc000
> PC is at drm_atomic_helper_update_legacy_modeset_state+0x204/0x20c
> LR is at drm_atomic_helper_commit_modeset_disables+0x1c0/0x394
> pc : [<ffffffc0003e6d18>] lr : [<ffffffc0003e8214>] pstate: 20000145
> sp : ffffffc9755df430
> x29: ffffffc9755df430 x28: ffffffc975703600
> x27: 0000000000000000 x26: ffffffc976253960
> x25: ffffffc976254040 x24: ffffffc000819000
> x23: ffffffc000689ea0 x22: ffffffc976251800
> x21: ffffffc976251800 x20: 0000000000000000
> x19: ffffffc9766b1f80 x18: 00000000715fe015
> x17: 0000007fb4b855b0 x16: 0000000000000220
> x15: 0000000000000001 x14: 0ffffffffffffffe
> x13: 0000000000000008 x12: 0101010101010101
> x11: ffffffc000964000 x10: ffffffc0009d2000
> x9 : 0000000000000000 x8 : ffffffc97ff5f700
> x7 : ffffffc97566cb80 x6 : ffffffc9766b1700
> x5 : ffffffc975665100 x4 : 0000000000000000
> x3 : ffffffc976253960 x2 : ffffffc97566cd00
> x1 : ffffffc976253900 x0 : 0000000000000000
>                  
> ---[ end trace 9fe289f798e7178e ]---
> Call trace:
> [<ffffffc0003e6d18>] drm_atomic_helper_update_legacy_modeset_state+0x204/0x20c
> [<ffffffc0003e8214>] drm_atomic_helper_commit_modeset_disables+0x1c0/0x394
> [<ffffffc0003e84c8>] drm_atomic_helper_commit+0xe0/0x150
> [<ffffffc00040bcc0>] drm_atomic_commit+0x40/0x6c
> [<ffffffc0003e92c0>] restore_fbdev_mode+0x294/0x2d4
> [<ffffffc0003eb6ec>] drm_fb_helper_restore_fbdev_mode_unlocked+0x34/0x8c
> [<ffffffc0003eb770>] drm_fb_helper_set_par+0x2c/0x58
> [<ffffffc000378048>] fbcon_init+0x4d4/0x534
> [<ffffffc0003b44f4>] visual_init+0xac/0x104
> [<ffffffc0003b63f8>] do_bind_con_driver+0x16c/0x398
> [<ffffffc0003b6968>] do_take_over_console+0xd8/0x1f4
> [<ffffffc00037811c>] do_fbcon_takeover+0x74/0xf8
> [<ffffffc00037c5cc>] fbcon_event_notify+0x8a4/0x8f8
> [<ffffffc0000d19f0>] notifier_call_chain+0x4c/0x88
> [<ffffffc0000d1d78>] __blocking_notifier_call_chain+0x44/0x74
> [<ffffffc0000d1dbc>] blocking_notifier_call_chain+0x14/0x1c
> [<ffffffc00037d614>] fb_notifier_call_chain+0x1c/0x24
> [<ffffffc00037f8a8>] register_framebuffer+0x1c0/0x2ac
> [<ffffffc0003eb9f8>] drm_fb_helper_initial_config+0x25c/0x3ec
> [<ffffffc0003ec28c>] drm_fbdev_cma_init+0x98/0x134
> [<ffffffbffc006780>] hdlcd_drm_bind+0x180/0x498 [hdlcd]
> [<ffffffc0004158e0>] try_to_bring_up_master.part.5+0xd4/0x118
> [<ffffffc0004159e8>] component_master_add_with_match+0xc4/0x148
> [<ffffffc000415a7c>] component_master_add+0x10/0x18
> [<ffffffbffc0065ec>] hdlcd_probe+0x14/0x28 [hdlcd]
> [<ffffffc00041c504>] platform_drv_probe+0x54/0xc0
> [<ffffffc00041a9b0>] driver_probe_device+0x1ec/0x2e8
> [<ffffffc00041ab48>] __driver_attach+0x9c/0xa0
> [<ffffffc000418bcc>] bus_for_each_dev+0x58/0x98
> [<ffffffc00041a41c>] driver_attach+0x20/0x28
> [<ffffffc00041a058>] bus_add_driver+0x1c8/0x22c
> [<ffffffc00041b3d0>] driver_register+0x68/0x108
> [<ffffffc00041c408>] __platform_driver_register+0x4c/0x54
> [<ffffffbffc00b018>] hdlcd_init+0x18/0x30 [hdlcd]
> [<ffffffc00008293c>] do_one_initcall+0x90/0x1a8
> [<ffffffc0001424dc>] do_init_module+0x60/0x1c8
> [<ffffffc00011d364>] load_module+0x1554/0x1c98
> [<ffffffc00011dc64>] SyS_finit_module+0x7c/0x88
> [<ffffffc000085cb0>] el0_svc_naked+0x24/0x28
>
>
> The line that triggers the warning is:
>
> 674:			WARN_ON(!connector->encoder->crtc);
>
> As far as I can see the encoder->crtc value is being set to a non-NULL value only
> in two places:
>   - in drm_atomic_helper_update_legacy_modeset_state() after WARN_ON()
> 		encoder->crtc = connector->state->crtc;
>   - in drm_crtc_helper_set_config(drm_mode_set *set):
> 		encoder->crtc = new_crtc;
>
> Nothing in the call path from drm_atomic_commit() calls crtc_funcs->set_config() or
> drm_crtc_helper_set_config() directly, so the question is if this WARN() is actually
> valid.
>
> Call path from drm_atomic_commit:
>
> drm_atomic_helper_commit()
>    - drm_atomic_helper_prepare_planes()
>    - drm_atomic_helper_swap_state()
>    - drm_atomic_helper_commit_modeset_disables()
>       - disable_outputs()
>       - drm_atomic_helper_update_legacy_modeset_state()
> 	- WARN_ON(!connector->encoder->crtc)
>
> Best regards,
> Liviu
>
Hi Liviu
       I solved this problem by following change, you can check if your 
driver do the same things:
        drivers/gpu/drm/bridge/dw_hdmi.c:
           -       hdmi->connector.encoder = encoder;
          +//     hdmi->connector.encoder = encoder;

drm_mode_connector_attach_encoder(&hdmi->connector, encoder);

      I found some other drivers set connector.encoder before 
drm_mode_connector_attach_encoder, some are not.

      drm_mode_connector_attach_encoder already describe the link of 
connector and encoder,
so I think "connector.encoder = encoder" is not needed, is that right?

Thanks.

-- 
Ｍark Yao

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