<div dir="ltr"><div dir="ltr"> </div> <div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Thu, Jun 19, 2025 at 7:08 AM Maxime Ripard <<a href="mailto:mripard@kernel.org">mripard@kernel.org</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Wed, Jun 18, 2025 at 04:45:31PM -0400, Anusha Srivatsa wrote: > On Wed, Jun 18, 2025 at 11:48 AM Anusha Srivatsa <<a href="mailto:asrivats@redhat.com" target="_blank">asrivats@redhat.com</a>> > wrote: > > On Wed, Jun 18, 2025 at 4:23 AM Maxime Ripard <<a href="mailto:mripard@kernel.org" target="_blank">mripard@kernel.org</a>> 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 <<a href="mailto:asrivats@redhat.com" target="_blank">asrivats@redhat.com</a>> wrote: > >> > > >> > > On Thu, Jun 12, 2025 at 3:24 AM Francesco Dolcini < > >> <a href="mailto:francesco@dolcini.it" target="_blank">francesco@dolcini.it</a>> > >> > > 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. </blockquote><div> </div><div>Sure!</div><div><a class="gmail_plusreply" id="plusReplyChip-0" href="mailto:francesco@dolcini.it" tabindex="-1">@Francesco Dolcini</a> Sending a fix with needed code reorder in a day or two.</div><div> </div><div>Anusha </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> Maxime </blockquote></div></div>