linux-kernel - Re: [PATCH] drm/omap: dsi: Fix deferred probe warnings

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Message-Id: <64CDFAA9-4CA3-4557-9C84-E563600B810C@goldelico.com>
Date:   Wed, 12 Apr 2023 11:00:12 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        Tomi Valkeinen <tomba@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Sebastian Reichel <sre@...nel.org>,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/omap: dsi: Fix deferred probe warnings


> Am 12.04.2023 um 10:50 schrieb Laurent Pinchart <laurent.pinchart@...asonboard.com>:
> 
> Hi Tony,
> 
> Thank you for the patch.
> 
> On Wed, Apr 12, 2023 at 10:39:53AM +0300, Tony Lindgren wrote:
>> We may not have dsi->dsidev initialized during probe, and that can
>> lead into various dsi related warnings as omap_dsi_host_detach() gets
>> called with dsi->dsidev set to NULL.
>> 
>> The warnings can be "Fixed dependency cycle(s)" followed by a
>> WARNING: CPU: 0 PID: 787 at drivers/gpu/drm/omapdrm/dss/dsi.c:4414.
> 
> How can this happen ? I assume .detach() can't be called without a
> priori successful call to .attach(), that that sets dsi->dsidev.

I have a similar patch (not submitted because it looks like a workaround) in our LetuxOS kernel:

https://git.goldelico.com/?p=letux-kernel.git;a=commitdiff;h=0656acb534439d4546b33826de62694e1df1b8ad

There I had commented:

dsi_init_output() called by dsi_probe() may fail. In that
case mipi_dsi_host_unregister() is called which may call
omap_dsi_host_detach() with uninitialized dsi->dsidev
because omap_dsi_host_attach() was never called before.

This happens if the panel driver asks for an EPROBE_DEFER.

So let's suppress the WARN() in this special case.

[    7.416759] WARNING: CPU: 0 PID: 32 at drivers/gpu/drm/omapdrm/dss/dsi.c:4419 omap_dsi_host_detach+0x3c/0xbc [omapdrm]
[    7.436053] Modules linked in: ina2xx_adc snd_soc_ts3a227e bq2429x_charger bq27xxx_battery_i2c(+) bq27xxx_battery ina2xx tca8418_keypad as5013(+) omapdrm hci_uart cec palmas_pwrbutton btbcm bmp280_spi palmas_gpadc bluetooth usb3503 ecdh_generic bmc150_accel_i2c bmg160_i2c ecc bmc150_accel_core bmg160_core bmc150_magn_i2c bmp280_i2c bmc150_magn bno055 industrialio_triggered_buffer bmp280 kfifo_buf snd_soc_omap_aess display_connector drm_kms_helper syscopyarea snd_soc_omap_mcbsp snd_soc_ti_sdma sysfillrect ti_tpd12s015 sysimgblt fb_sys_fops wwan_on_off snd_soc_gtm601 generic_adc_battery drm snd_soc_w2cbw003_bt industrialio drm_panel_orientation_quirks pwm_bl pwm_omap_dmtimer ip_tables x_tables ipv6 autofs4
[    7.507068] CPU: 0 PID: 32 Comm: kworker/u4:2 Tainted: G        W          6.1.0-rc3-letux-lpae+ #11107
[    7.516964] Hardware name: Generic OMAP5 (Flattened Device Tree)
[    7.523284] Workqueue: events_unbound deferred_probe_work_func
[    7.529456]  unwind_backtrace from show_stack+0x10/0x14
[    7.534972]  show_stack from dump_stack_lvl+0x40/0x4c
[    7.540315]  dump_stack_lvl from __warn+0xb0/0x164
[    7.545379]  __warn from warn_slowpath_fmt+0x70/0x9c
[    7.550625]  warn_slowpath_fmt from omap_dsi_host_detach+0x3c/0xbc [omapdrm]
[    7.558137]  omap_dsi_host_detach [omapdrm] from mipi_dsi_remove_device_fn+0x10/0x20
[    7.566376]  mipi_dsi_remove_device_fn from device_for_each_child+0x60/0x94
[    7.573729]  device_for_each_child from mipi_dsi_host_unregister+0x20/0x54
[    7.580992]  mipi_dsi_host_unregister from dsi_probe+0x5d8/0x744 [omapdrm]
[    7.588315]  dsi_probe [omapdrm] from platform_probe+0x58/0xa8
[    7.594542]  platform_probe from really_probe+0x144/0x2ac
[    7.600249]  really_probe from __driver_probe_device+0xc4/0xd8
[    7.606411]  __driver_probe_device from driver_probe_device+0x3c/0xb8
[    7.613216]  driver_probe_device from __device_attach_driver+0x58/0xbc
[    7.620115]  __device_attach_driver from bus_for_each_drv+0xa0/0xb4
[    7.626737]  bus_for_each_drv from __device_attach+0xdc/0x150
[    7.632808]  __device_attach from bus_probe_device+0x28/0x80
[    7.638792]  bus_probe_device from deferred_probe_work_func+0x84/0xa0
[    7.645595]  deferred_probe_work_func from process_one_work+0x1a4/0x2d8
[    7.652587]  process_one_work from worker_thread+0x214/0x2b8
[    7.658567]  worker_thread from kthread+0xe4/0xf0
[    7.663542]  kthread from ret_from_fork+0x14/0x1c
[    7.668515] Exception stack(0xf01b5fb0 to 0xf01b5ff8)
[    7.673827] 5fa0:                                     00000000 00000000 00000000 00000000
[    7.682435] 5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    7.691038] 5fe0: 00000000 00000000 00000000 00000000 00000013 00000000

Hope this helps to find the real cause.

BR,
Nikolaus