drm/panel/panel-simple v6.16-rc1 WARNING regression
Anusha Srivatsa
asrivats at redhat.com
Wed Jun 18 20:45:31 UTC 2025
On Wed, Jun 18, 2025 at 11:48 AM Anusha Srivatsa <asrivats at redhat.com>
wrote:
>
>
> On Wed, Jun 18, 2025 at 4:23 AM Maxime Ripard <mripard at kernel.org> wrote:
>
>> On Wed, Jun 18, 2025 at 10:51:58AM +0200, Luca Ceresoli wrote:
>> > Hello Anusha, Francesco,
>> >
>> > On Tue, 17 Jun 2025 11:17:20 -0500
>> > Anusha Srivatsa <asrivats at redhat.com> wrote:
>> >
>> > > 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....
>> >
>> > Reading the panel-simple.c code, the handling of the panel_dsi
>> > descriptor feels a bit hacky, and the recent change to
>> > devm_drm_panel_alloc() breaks it easily. Perhaps it would be cleaner to
>> > assess the whole descriptor before ding any allocation/init.
>> >
>> > You're right tat panel_dpi_probe() needs the panel, but it's only at the
>> > very end, to assign the descriptor:
>> >
>> > panel->desc = desc;
>> >
>> > I think a good fix would be to clean it up by having:
>> >
>> > * panel_dpi_probe() not take a panel pointer but rather returning a
>> > filled descriptor
>> > * panel_simple_probe() call panel_dpi_probe() early [before
>> > devm_drm_panel_alloc()] and get the filled descriptor
>> > * call devm_drm_panel_alloc() with that descriptor in the panel-dsi
>> > case, or with the good old descriptor otherwise
>> >
>> > As a good side effect, it would get rid of a case where
>> > devm_drm_panel_alloc() is called with a Unknown connector type.
>> >
>> > Anusha, does it look like a good plan?
>>
>> It is, and I'd even go one step further. Like you said, panel_dpi_probe
>> kind of exists to allocate and initialize the panel descriptor, and is
>> called on the descriptor being equal to the (uninitialized) panel_dpi
>> global variable.
>>
>> We should also get rid of that hack, so do something like creating a
>> function that returns the descriptor, and is indeed called first in
>> panel_simple_probe. It first calls of_device_get_match_data(), and if
>> there's no match, and if the device is compatible with panel-dpi, then
>> it calls panel_dpi_probe (we should probably change that name too). That
>> way, we can get rid of the panel_dpi variable entirely.
>>
>>
> Thanks Luca and Maxime.
> To summarize:
> 1. add a function like of_device_get_simple_dsi_match_data() which calls
> of_device_get_match_data(). if the device is compatible with panel-dpi,
> call
> panel-dpi-probe()
> 3. Change panel_dpi_probe() to return the panel descriptor
> 4. call devm_drm_panel_alloc()
>
>
Looking deeper it looks like I have some gaps in my understanding.
panel_simple_platform_probe()
already checks of_device_get_match_data() to call panel_simple_probe(). At
this point the change suggested is
to have to call it again to check if it is compatible with panel-dpi? If I
understand correctly panel_dpi is a fallback
and the only place the decision to probe panel_dpi() is with the hack.
Thanks,
> Anusha
>
>> Maxime
>>
>
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