drm: Bogus WARN() in drm_atomic_helper_update_legacy_modeset_state() ?

[Mark yao]

On 2015年11月12日 18:36, Liviu Dudau wrote:
> 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
Hi Liviu
      drivers/gpu/drm/i2c/tda998x_drv.c do the same things:
             priv->connector.encoder = &priv->encoder;
drm_mode_connector_attach_encoder(&priv->connector, &priv->encoder);

      I believe must be same problem.

Thanks.

-- 
Ｍark Yao