drm/panel/panel-simple v6.16-rc1 WARNING regression

[Anusha Srivatsa]

On Thu, Jun 12, 2025 at 3:24 AM Francesco Dolcini <francesco at dolcini.it>
wrote:

> Hello all,
>
> Commit de04bb0089a9 ("drm/panel/panel-simple: Use the new allocation in
> place of devm_kzalloc()")
> from 6.16-rc1 introduced a regression with this warning during probe
> with panel dpi described in the DT.
>
> A revert solves the issue.
>
> The issue is that connector_type is set to DRM_MODE_CONNECTOR_DPI in
> panel_dpi_probe() that after that change is called after
> devm_drm_panel_alloc().
>
> I am not sure if there are other implication for this change in the call
> ordering, apart the one that triggers this warning.
>
> [   12.089274] ------------[ cut here ]------------
> [   12.089303] WARNING: CPU: 0 PID: 96 at
> drivers/gpu/drm/bridge/panel.c:377 devm_drm_of_get_bridge+0xac/0xb8
> [   12.130808] Modules linked in: v4l2_jpeg pwm_imx27(+) imx_vdoa
> gpu_sched panel_simple imx6_media(C) imx_media_common
> (C) videobuf2_dma_contig pwm_bl gpio_keys v4l2_mem2mem fuse ipv6 autofs4
> [   12.147774] CPU: 0 UID: 0 PID: 96 Comm: kworker/u8:3 Tainted: G
>  C          6.16.0-rc1+ #1 PREEMPT
> [   12.157446] Tainted: [C]=CRAP
> [   12.160418] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> [   12.166953] Workqueue: events_unbound deferred_probe_work_func
> [   12.172805] Call trace:
> [   12.172815]  unwind_backtrace from show_stack+0x10/0x14
> [   12.180598]  show_stack from dump_stack_lvl+0x68/0x74
> [   12.185674]  dump_stack_lvl from __warn+0x7c/0xe0
> [   12.190407]  __warn from warn_slowpath_fmt+0x1b8/0x1c0
> [   12.195567]  warn_slowpath_fmt from devm_drm_of_get_bridge+0xac/0xb8
> [   12.201949]  devm_drm_of_get_bridge from imx_pd_probe+0x58/0x164
> [   12.207976]  imx_pd_probe from platform_probe+0x5c/0xb0
> [   12.213220]  platform_probe from really_probe+0xd0/0x3a4
> [   12.218551]  really_probe from __driver_probe_device+0x8c/0x1d4
> [   12.224486]  __driver_probe_device from driver_probe_device+0x30/0xc0
> [   12.230942]  driver_probe_device from __device_attach_driver+0x98/0x10c
> [   12.237572]  __device_attach_driver from bus_for_each_drv+0x90/0xe4
> [   12.243854]  bus_for_each_drv from __device_attach+0xa8/0x1c8
> [   12.249614]  __device_attach from bus_probe_device+0x88/0x8c
> [   12.255285]  bus_probe_device from deferred_probe_work_func+0x8c/0xcc
> [   12.261739]  deferred_probe_work_func from process_one_work+0x154/0x2dc
> [   12.268371]  process_one_work from worker_thread+0x250/0x3f0
> [   12.274043]  worker_thread from kthread+0x12c/0x24c
> [   12.278940]  kthread from ret_from_fork+0x14/0x28
> [   12.283660] Exception stack(0xd0be9fb0 to 0xd0be9ff8)
> [   12.288720] 9fa0:                                     00000000 00000000
> 00000000 00000000
> [   12.296906] 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000
> 00000000 00000000
> [   12.305089] 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> [   12.312050] ---[ end trace 0000000000000000 ]---
>
> #regzbot ^introduced: de04bb0089a96cc00d13b12cbf66a088befe3057
>
> Any advise?
>
> Hey Francesco!

This mail reached my spam and I hadn't realised till today. Thanks for
bringing this to attention.

Thinking out loud here: If we called dpi_probe() before allocating the
panel using devm_drm_panel_alloc()
then we would have the connector type. But  dpi_probe() needs the panel to
be allocated....

We could actually hardcode the connector type to DRM_MODE_CONNECTOR_DPI....
Looking at panel_dpi_probe(), it guesses the connector_type:

/* We do not know the connector for the DT node, so guess it
*/	desc->connector_type
<https://elixir.bootlin.com/linux/v6.16-rc2/C/ident/connector_type> =
DRM_MODE_CONNECTOR_DPI
<https://elixir.bootlin.com/linux/v6.16-rc2/C/ident/DRM_MODE_CONNECTOR_DPI>;


Reverting will improve the end user experience but if the fix can be quick,
we can
avoid dropping the change

Thanks,
Anusha


> Francesco
>
>
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