drm: Bogus WARN() in drm_atomic_helper_update_legacy_modeset_state() ?

[Liviu Dudau]

On Thu, Nov 12, 2015 at 04:32:33PM +0800, Mark yao wrote:
>    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?

I'll have a look, thanks for pointing this. However, my setup uses the tda998x driver for encoder, so I will
have to go look there rather than in my driver.

Best regards,
Liviu

> 
>    Thanks.
> 
>  --
>  Ｍark Yao

-- 
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