On Tue, 25 Nov 2025, Daniel Thompson wrote: > On Tue, Nov 25, 2025 at 09:24:26AM +0100, Michael Grzeschik wrote: > > On Tue, Nov 18, 2025 at 12:52:14PM +0000, Daniel Thompson wrote: > > > On Fri, Nov 14, 2025 at 02:09:56PM +0000, Mark Brown wrote: > > > > On Thu, Jul 31, 2025 at 10:47:18AM +0200, Michael Grzeschik wrote: > > > > > Currently when calling pwm_apply_might_sleep in the probe routine > > > > > the pwm will be configured with an not fully defined state. > > > > > > > > > > The duty_cycle is not yet set in that moment. There is a final > > > > > backlight_update_status call that will have a properly setup state. > > > > > However this change in the backlight can create a short flicker if the > > > > > backlight was already preinitialised. > > > > > > > > I'm seeing the libre.computer Renegade Elite producing warnings during > > > > boot in -next which bisect to this patch. The warnings are: > > > > > > > > [ 24.175095] input: adc-keys as > > > > /devices/platform/adc-keys/input/input1 > > > > [ 24.176612] ------------[ cut here ]------------ > > > > [ 24.177048] WARNING: CPU: 0 PID: 0 at kernel/context_tracking.c:127 > > > > ct_kernel_exit.constprop.0+0x98/0xa0 > > > > > > > > ... > > > > > > > > [ 24.190106] Call trace: > > > > [ 24.190325] ct_kernel_exit.constprop.0+0x98/0xa0 (P) > > > > [ 24.190775] ct_idle_enter+0x10/0x20 > > > > [ 24.191096] cpuidle_enter_state+0x1fc/0x320 > > > > [ 24.191476] cpuidle_enter+0x38/0x50 > > > > [ 24.191802] do_idle+0x1e4/0x260 > > > > [ 24.192094] cpu_startup_entry+0x34/0x3c > > > > [ 24.192444] rest_init+0xdc/0xe0 > > > > [ 24.192734] console_on_rootfs+0x0/0x6c > > > > [ 24.193082] __primary_switched+0x88/0x90 > > > > [ 24.193445] ---[ end trace 0000000000000000 ]--- > > > > > > > > which seems a little surprising but there is some console stuff there > > > > that looks relevant. > > > > > > > > Full log: > > > > > > > > https://lava.sirena.org.uk/scheduler/job/2086528#L897 > > > > > > Michael, reading these logs it looks to me like the underlying oops > > > is this backtrace (which makes a lot more sense given the code you > > > altered): > > > > > > [ 24.133631] Call trace: > > > [ 24.133853] pwm_backlight_probe+0x830/0x868 [pwm_bl] (P) > > > [ 24.134341] platform_probe+0x5c/0xa4 > > > [ 24.134679] really_probe+0xbc/0x2c0 > > > [ 24.135001] __driver_probe_device+0x78/0x120 > > > [ 24.135391] driver_probe_device+0x3c/0x154 > > > [ 24.135765] __driver_attach+0x90/0x1a0 > > > [ 24.136111] bus_for_each_dev+0x7c/0xdc > > > [ 24.136462] driver_attach+0x24/0x38 > > > [ 24.136785] bus_add_driver+0xe4/0x208 > > > [ 24.137124] driver_register+0x68/0x130 > > > [ 24.137468] __platform_driver_register+0x24/0x30 > > > [ 24.137888] pwm_backlight_driver_init+0x20/0x1000 [pwm_bl] > > > [ 24.138389] do_one_initcall+0x60/0x1d4 > > > [ 24.138735] do_init_module+0x54/0x23c > > > [ 24.139073] load_module+0x1760/0x1cf0 > > > [ 24.139407] init_module_from_file+0x88/0xcc > > > [ 24.139787] __arm64_sys_finit_module+0x1bc/0x338 > > > [ 24.140207] invoke_syscall+0x48/0x104 > > > [ 24.140549] el0_svc_common.constprop.0+0x40/0xe0 > > > [ 24.140970] do_el0_svc+0x1c/0x28 > > > [ 24.141268] el0_svc+0x34/0xec > > > [ 24.141548] el0t_64_sync_handler+0xa0/0xf0 > > > [ 24.141920] el0t_64_sync+0x198/0x19c > > > > > > Should we back out the patch for now? > > > > I would be fine with that. But actually I would like to see the > > proof that without the patch, this backtrace will not trigger. > > Looking through the codepath, I could not directly find a case > > where this should happen. > > I took a look at the logs Mark provided and I think the problem > is a divide-by-zero caused by calling pwm_backlight_brightness_default() > when state.period is zero. > > It emerges as a BRK because the compiler recognised there is undefined > behaviour. The zero that we divide by comes from a ternary condition in > fls(). The compiler recognises one of the conditional code paths will > result in undefined behaviour so, it doesn't need to generating code for > the bad code path, it just injects a brk instruction. > > > > Mark, is there a way to rerun this without my patch? > > I have to admit I thought this was why Mark provided a bisect log! > > Anyhow, unless someone can refute the analysis above I do think we need > to pull the patch.
Un-applied now, thanks. -- Lee Jones [李琼斯]
