Re: [PATCH v6 0/7] HID: asus: Fix ASUS ROG Laptop's Keyboard backlight handling

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Fri, 17 Oct 2025, Antheas Kapenekakis wrote:
> On Thu, 16 Oct 2025 at 18:16, Antheas Kapenekakis <lkml@antheas.dev> wrote:
> >
> > On Thu, 16 Oct 2025 at 17:09, Ilpo Järvinen
> > <ilpo.jarvinen@linux.intel.com> wrote:
> > >
> > > On Thu, 16 Oct 2025, Antheas Kapenekakis wrote:
> > > > On Thu, 16 Oct 2025 at 13:57, Denis Benato <benato.denis96@gmail.com> wrote:
> > > > > On 10/13/25 22:15, Antheas Kapenekakis wrote:
> > > > > > This is a two part series which does the following:
> > > > > >   - Clean-up init sequence
> > > > > >   - Unify backlight handling to happen under asus-wmi so that all Aura
> > > > > >     devices have synced brightness controls and the backlight button works
> > > > > >     properly when it is on a USB laptop keyboard instead of one w/ WMI.
> > > > > >
> > > > > > For more context, see cover letter of V1. Since V5, I removed some patches
> > > > > > to make this easier to merge.
> > > > > >
> > > > > > All comments with these patches had been addressed since V4.
> > > > > I have loaded this patchset for users of asus-linux project to try out.
> > > > >
> > > > > One of them opened a bug report about a kernel bug that happens
> > > > > consistently when closing the lid of his laptop [1].
> > > > >
> > > > > He also sent another piece of kernel log, but didn't specify anything more
> > > > > about this [2].
> > > > >
> > > > > [1] https://pastebin.com/akZx1w10
> > > > > [2] https://pastebin.com/sKdczPgf
> > > >
> > > > Can you provide a link to the bug report? [2] seems unrelated.
> > > >
> > > > As for [1], it looks like a trace that stems from a sysfs write to
> > > > brightness stemming from userspace that follows the same chain it
> > > > would on a stock kernel and times out. Is it present on a stock
> > > > kernel?
> > > >
> > > > Ilpo should know more about this, could the spinlock be interfering?
> > >
> > > [1] certainly seems to do schedule() from do_kbd_led_set() so it's not
> > > possible to use spinlock there.
> > >
> > > So we're back to what requires the spinlock? And what the spinlock
> > > protects?
> >
> > For that invocation, since it is coming from the cdev device owned by
> > asus_wmi, it protects asus_ref.listeners under do_kbd_led_set.
> > asus_wmi is protected by the fact it is owned by that device. Spinlock
> > is not required in this invocation due to not being an IRQ.
> >
> > Under asus_hid_event (second to last patch), which is called from an
> > IRQ, a spinlock is required for protecting both listeners and the
> > asus_ref.asus, and I suspect that scheduling from an IRQ is not
> > allowed either. Is that correct?
> 
> So it is a bit tricky here. When the IRQ fires, it needs to know
> whether asus-wmi will handle the keyboard brightness event so that it
> falls back to emitting it.
> 
> If we want it to know for sure, it needs to access asus_wmi, so it
> needs a spinlock or an IRQ friendly lock. This way, currently,
> asus_hid_event will return -EBUSY if there is no led device so the
> event propagates through hid.
>
> If we say that it is good enough to know that it was compiled with
> IS_REACHABLE(CONFIG_ASUS_WMI), ie the actual implementation of
> asus_hid_event in asus-wmi will never return an error, then,
> asus_hid_event can schedule a task to fire the event without a lock,
> and that task can use a normal locking primitive.
> 
> If the task needs to be assigned to a device or have a handle,
> asus_hid_listener can be provided to asus_hid_event, so that it is
> owned by the calling device.
> 
> What would the appropriate locking primitive be in this case?

If you can move the non-check content out of asus_hid_event(), then you 
can nest mutex & spinlock for updating asus_ref. On reader side, 
asus_hid_event() only takes the spinlock and the rest of the readers 
(non-irq ones) can take just the mutex.


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