drm/panel/panel-simple v6.16-rc1 WARNING regression
Anusha Srivatsa
asrivats at redhat.com
Mon Jun 23 16:56:59 UTC 2025
On Thu, Jun 19, 2025 at 7:08 AM Maxime Ripard <mripard at kernel.org> wrote:
> On Wed, Jun 18, 2025 at 04:45:31PM -0400, Anusha Srivatsa wrote:
> > 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.
>
> I'm sure you can figure something out. And feel free to send me patches
> for a private review if you feel more comfortable that way.
>
>
Sure!
@Francesco Dolcini <francesco at dolcini.it> Sending a fix with needed code
reorder in a day or two.
Anusha
> Maxime
>
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