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Date: Thu, 30 May 2024 13:44:07 -0700
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: "Limonciello, Mario" <mario.limonciello@amd.com>,
	Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>,
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	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	linux-kernel@vger.kernel.org,
	Chris Bainbridge <chris.bainbridge@gmail.com>, hughsient@gmail.com,
	linux-input@vger.kernel.org
Subject: Re: [PATCH v2] drm/client: Detect when ACPI lid is closed during
 initialization
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On Thu, May 30, 2024 at 11:07:53AM +0300, Dmitry Baryshkov wrote:
> On Thu, 30 May 2024 at 07:41, Limonciello, Mario
> <mario.limonciello@amd.com> wrote:
> >
> >
> > >> Also a direct acpi_lid_open() call seems a bit iffy. But I guess if
> > >> someone needs this to work on non-ACPI system they get to figure out
> > >> how to abstract it better. acpi_lid_open() does seem to return != 0
> > >> when ACPI is not supported, so at least it would err on the side
> > >> of enabling everything.
> > >
> > > Thanks. I was going to comment, but you got it first. I think a proper
> > > implementation should check for SW_LID input device instead of simply
> > > using acpi_lid_open(). This will handle the issue for other,
> > > non-ACPI-based laptops.
> > >
> >
> > Can you suggest how this would actually work?  AFAICT the only way to
> > discover if input devices support SW_LID would be to iterate all the
> > input devices in the kernel and look for whether ->swbit has SW_LID set.
> >
> > This then turns into a dependency problem of whether any myriad of
> > drivers have started to report SW_LID.  It's also a state machine
> > problem because other drivers can be unloaded at will.
> >
> > And then what do you if more than one sets SW_LID?
> 
> It might be easier to handle this in the input subsystem. For example
> by using a refcount-like variable which handles all the LIDs and
> counts if all of them are closed. Or if any of the LIDs is closed.

Yes, install an input handler matching on EV_SW/SW_LID so you will get
notified when input devices capable of reporting SW_LID appear and
disappear and also when SW_LID event is being generated, and handle as
you wish. Something like

https://chromium.googlesource.com/chromiumos/third_party/kernel/+/40e9f6a991856ee7d504ac1ccd587e435775cfc4%5E%21/#F0

In practice I think it is pretty safe to assume only 1 lid for a
laptop/device.

Thanks.

-- 
Dmitry