Nouveau - May 2017 - [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open() invocations

Hi,

If my previous reply is not persuasive enough.
Let me do that in a different way.
> From: linux-acpi-owner at vger.kernel.org [mailto:linux-acpi-owner at
vger.kernel.org] On Behalf Of Zheng,
> Lv
> Subject: RE: [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open()
invocations
> 
> Hi,
> 
> > From: Benjamin Tissoires [mailto:benjamin.tissoires at gmail.com]
> > Subject: Re: [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open()
invocations
> >
> > On Tue, May 9, 2017 at 9:02 AM, Lv Zheng <lv.zheng at intel.com>
wrote:
> > > Since notification side has been changed to always notify kernel
listeners
> > > using _LID returning value. Now listeners needn't invoke
acpi_lid_open(),
> > > it should use a spec suggested control method lid device usage
model:
> > > register lid notification and use the notified value instead,
which is the
> > > only way to ensure the value is correct for
"button.lid_init_state=ignore"
> > > mode or other modes with "button.lid_fake_events=N"
specified.
> > >
> > > This patch fixes i915 driver to drop acpi_lid_open() user.
It's not
> > > possible to change nouveau_connector.c user using a simple way
now. So this
> > > patch only marks acpi_lid_open() as deprecated to accelerate this
process
> > > by indicating this change to the nouveau developers.
> >
> > If  the only 2 users of acpi_lid_open() are intel and nouveau, and if
> > they should rely on the value stored in the input node, not the one
> > exported by the _LID method (which can be wrong on some platforms),
> > how about simply changing the implementation of acpi_lid_open() to
> > fetch the value from the input node directly?
If acpi_lid_open() returns stored value in input node,
then it actually returns the value we notified to the input layer.
While i915 and nouveau explicitly do not trust that value and invoke
acpi_lid_open().

For button.lid_init_state=method, PATCH 4/5 is useless as the values are same.

However in my reply of PATCH 2.
I explained the difference of method/close, for the same reason, we can also
sense the difference of method/open.
The difference then can explain the usefulness of open/close modes.

Given open/close modes are all useful:
button.lid_init_state=open
1. button driver sends open to input layer after boot/resume
2. i915/nouveau uses _LID return value after boot/resume
If _LID return value after boot/resume is "close", they are different.

button.lid_init_state=close
1. button driver sends close to input layer after boot/resume
2. i915/nouveau uses _LID return value after boot/resume
If _LID return value after boot/resume is "open", they are different.

The only way to be consistent to old i915/nouveau behavior is:
button.lid_init_state=open/close
1. button driver sends open/close to input layer after boot/resume
2. button driver sends _LID return value to i915 after boot/resume (PATCH 4)
So that i915 can just use the notified value in this patch (PATCH 5).
For nouveau, no change has been made for now, and as a concequence,
acpi_lid_open() is still kept but marked as deprecated.
> 
> See my reply of PATCH 4.
> It seems they trust _LID return value more than what we send to them.
> 
> We can actually send faked "open/close" to them when
button.lid_init_state=open/close is specified.
> 
> So these 2 patches [PATCH 4-5/5] are used to do a small cleanup for lid
event notifier APIs.
> I think they are not strictly related to the lid issues we are talking
about.
See Documentation/acpi/acpi-lid.txt:
The _LID control method is described to return the "current" lid
state.
However the word of "current" has ambiguity, some buggy AML tables
return
the lid state upon the last lid notification instead of returning the lid
state upon the last _LID evaluation.

In order to have acpi lid event notifier API compliant to the above mentioned
both "buggy" and "nonbuggy" implementation.
The ensured lid event model interface should be:
1. Lid event notifier listeners invokes acpi_lid_notifier_register().
2. And in the callback, uses _LID return value.
This is also the only possible way to combine "receiving lid notify"
and "evaluate _LID" into 1 single atomic operation.

So I trend to remove acpi_lid_open() and enforce the new API.

As a conclusion, PATCH 4-5
1. makes a hidden logic explicit - the lid event listeners always use _LID
return value. Less hidden logics should leave less chances of bugs.
2. is an implementation for our documented ACPI lid event model.
And the implementation is done in a regression safe way.

Thanks,
Lv
> 
> Cheers,
> Lv
> 
> >
> > Cheers,
> > Benjamin
> >
> > >
> > > Cc: <intel-gfx at lists.freedesktop.org>
> > > Cc: <nouveau at lists.freedesktop.org>
> > > Signed-off-by: Lv Zheng <lv.zheng at intel.com>
> > > ---
> > >  drivers/acpi/button.c             | 7 ++++++-
> > >  drivers/gpu/drm/i915/intel_lvds.c | 2 +-
> > >  2 files changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
> > > index 7ff3a75..50d7898 100644
> > > --- a/drivers/acpi/button.c
> > > +++ b/drivers/acpi/button.c
> > > @@ -348,7 +348,12 @@ int acpi_lid_notifier_unregister(struct
notifier_block *nb)
> > >  }
> > >  EXPORT_SYMBOL(acpi_lid_notifier_unregister);
> > >
> > > -int acpi_lid_open(void)
> > > +/*
> > > + * The intentional usage model is to register a lid notifier and
use the
> > > + * notified value instead. Directly evaluating _LID without
seeing a
> > > + * Notify(lid, 0x80) is not reliable.
> > > + */
> > > +int __deprecated acpi_lid_open(void)
> > >  {
> > >         if (!lid_device)
> > >                 return -ENODEV;
> > > diff --git a/drivers/gpu/drm/i915/intel_lvds.c
b/drivers/gpu/drm/i915/intel_lvds.c
> > > index 9ca4dc4..8ca9080 100644
> > > --- a/drivers/gpu/drm/i915/intel_lvds.c
> > > +++ b/drivers/gpu/drm/i915/intel_lvds.c
> > > @@ -548,7 +548,7 @@ static int intel_lid_notify(struct
notifier_block *nb, unsigned long val,
> > >         /* Don't force modeset on machines where it causes a
GPU lockup */
> > >         if (dmi_check_system(intel_no_modeset_on_lid))
> > >                 goto exit;
> > > -       if (!acpi_lid_open()) {
> > > +       if (!val) {
> > >                 /* do modeset on next lid open event */
> > >                 dev_priv->modeset_restore =
MODESET_ON_LID_OPEN;
> > >                 goto exit;
> > > --
> > > 2.7.4
> > >
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe
linux-acpi" in
> > > the body of a message to majordomo at vger.kernel.org
> > > More majordomo info at 
http://vger.kernel.org/majordomo-info.html
> &~&+-wmbZr^nrzh&Gh(
> j"mzfh~m

Hi Lv,

I am trying to reduce the number of parallel discussion we have on the
same subject, but there is something here I can't let you have.

On Fri, May 12, 2017 at 8:08 AM, Zheng, Lv <lv.zheng at intel.com>
wrote:
> Hi,
>
> If my previous reply is not persuasive enough.
> Let me do that in a different way.
>
>> From: linux-acpi-owner at vger.kernel.org [mailto:linux-acpi-owner at
vger.kernel.org] On Behalf Of Zheng,
>> Lv
>> Subject: RE: [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open()
invocations
>>
>> Hi,
>>
>> > From: Benjamin Tissoires [mailto:benjamin.tissoires at gmail.com]
>> > Subject: Re: [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open()
invocations
>> >
>> > On Tue, May 9, 2017 at 9:02 AM, Lv Zheng <lv.zheng at
intel.com> wrote:
>> > > Since notification side has been changed to always notify
kernel listeners
>> > > using _LID returning value. Now listeners needn't invoke
acpi_lid_open(),
>> > > it should use a spec suggested control method lid device
usage model:
>> > > register lid notification and use the notified value instead,
which is the
>> > > only way to ensure the value is correct for
"button.lid_init_state=ignore"
>> > > mode or other modes with "button.lid_fake_events=N"
specified.
>> > >
>> > > This patch fixes i915 driver to drop acpi_lid_open() user.
It's not
>> > > possible to change nouveau_connector.c user using a simple
way now. So this
>> > > patch only marks acpi_lid_open() as deprecated to accelerate
this process
>> > > by indicating this change to the nouveau developers.
>> >
>> > If  the only 2 users of acpi_lid_open() are intel and nouveau, and
if
>> > they should rely on the value stored in the input node, not the
one
>> > exported by the _LID method (which can be wrong on some
platforms),
>> > how about simply changing the implementation of acpi_lid_open() to
>> > fetch the value from the input node directly?
>
> If acpi_lid_open() returns stored value in input node,
> then it actually returns the value we notified to the input layer.
> While i915 and nouveau explicitly do not trust that value and invoke
acpi_lid_open().
>
> For button.lid_init_state=method, PATCH 4/5 is useless as the values are
same.
>
> However in my reply of PATCH 2.
> I explained the difference of method/close, for the same reason, we can
also sense the difference of method/open.
> The difference then can explain the usefulness of open/close modes.
>
> Given open/close modes are all useful:
> button.lid_init_state=open
> 1. button driver sends open to input layer after boot/resume
> 2. i915/nouveau uses _LID return value after boot/resume
> If _LID return value after boot/resume is "close", they are
different.
>
> button.lid_init_state=close
> 1. button driver sends close to input layer after boot/resume
> 2. i915/nouveau uses _LID return value after boot/resume
> If _LID return value after boot/resume is "open", they are
different.
>
> The only way to be consistent to old i915/nouveau behavior is:
> button.lid_init_state=open/close
But these two modes are wrong in the absolute case:
- a laptop has no reasons for not being powered up with the lid
physically closed (wake on lan?) -> so open is an approximation
already made on good assumption that there is not a high chance of the
users powering/resuming the laptop with the lid closed
- in the "close" case, this setting works for docked laptops, but if
the laptop can be docked, it can also be undocked. And if you boot
with button.lid_init_state=close, undock your laptop, go into suspend,
resume -> the lid state is now "closed" while it should be opened.

So no, these are just workarounds. i915/nouveau expect the acpi/button
state to be reliable, or they should ignore it. But you can't fake
events when you are not absolutely sure of what is happening.
> 1. button driver sends open/close to input layer after boot/resume
> 2. button driver sends _LID return value to i915 after boot/resume (PATCH
4)
> So that i915 can just use the notified value in this patch (PATCH 5).
> For nouveau, no change has been made for now, and as a concequence,
acpi_lid_open() is still kept but marked as deprecated.
>
>>
>> See my reply of PATCH 4.
>> It seems they trust _LID return value more than what we send to them.
>>
>> We can actually send faked "open/close" to them when
button.lid_init_state=open/close is specified.
>>
>> So these 2 patches [PATCH 4-5/5] are used to do a small cleanup for lid
event notifier APIs.
>> I think they are not strictly related to the lid issues we are talking
about.
>
> See Documentation/acpi/acpi-lid.txt:
> The _LID control method is described to return the "current" lid
state.
> However the word of "current" has ambiguity, some buggy AML
tables return
> the lid state upon the last lid notification instead of returning the lid
> state upon the last _LID evaluation.
>
> In order to have acpi lid event notifier API compliant to the above
mentioned both "buggy" and "nonbuggy" implementation.
> The ensured lid event model interface should be:
> 1. Lid event notifier listeners invokes acpi_lid_notifier_register().
> 2. And in the callback, uses _LID return value.
> This is also the only possible way to combine "receiving lid
notify" and "evaluate _LID" into 1 single atomic operation.
>
> So I trend to remove acpi_lid_open() and enforce the new API.
>
> As a conclusion, PATCH 4-5
> 1. makes a hidden logic explicit - the lid event listeners always use _LID
return value. Less hidden logics should leave less chances of bugs.
> 2. is an implementation for our documented ACPI lid event model.
> And the implementation is done in a regression safe way.
I understand all of that. But my point is still that on some
platforms, the lid acpi state is not reliable, and the code in
i915/nouveau is not made for those platforms. So the ideal solution is
to know which platforms are problematic and take the right decisions
having everything at hands. Just "fixing" the internal API won't
help
teaching these drivers to not make the assumption that the _LID acpi
call is always correct.

So yes, nouveau/i915 might need to be fixed, but IMO, fixing
acpi/button to report correct (true, accurate, actual, or physical if
you prefer) is the best, future proof way (minus platform quirks).

Cheers,
Benjamin
>
> Thanks,
> Lv
>
>>
>> Cheers,
>> Lv
>>
>> >
>> > Cheers,
>> > Benjamin
>> >
>> > >
>> > > Cc: <intel-gfx at lists.freedesktop.org>
>> > > Cc: <nouveau at lists.freedesktop.org>
>> > > Signed-off-by: Lv Zheng <lv.zheng at intel.com>
>> > > ---
>> > >  drivers/acpi/button.c             | 7 ++++++-
>> > >  drivers/gpu/drm/i915/intel_lvds.c | 2 +-
>> > >  2 files changed, 7 insertions(+), 2 deletions(-)
>> > >
>> > > diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
>> > > index 7ff3a75..50d7898 100644
>> > > --- a/drivers/acpi/button.c
>> > > +++ b/drivers/acpi/button.c
>> > > @@ -348,7 +348,12 @@ int acpi_lid_notifier_unregister(struct
notifier_block *nb)
>> > >  }
>> > >  EXPORT_SYMBOL(acpi_lid_notifier_unregister);
>> > >
>> > > -int acpi_lid_open(void)
>> > > +/*
>> > > + * The intentional usage model is to register a lid notifier
and use the
>> > > + * notified value instead. Directly evaluating _LID without
seeing a
>> > > + * Notify(lid, 0x80) is not reliable.
>> > > + */
>> > > +int __deprecated acpi_lid_open(void)
>> > >  {
>> > >         if (!lid_device)
>> > >                 return -ENODEV;
>> > > diff --git a/drivers/gpu/drm/i915/intel_lvds.c
b/drivers/gpu/drm/i915/intel_lvds.c
>> > > index 9ca4dc4..8ca9080 100644
>> > > --- a/drivers/gpu/drm/i915/intel_lvds.c
>> > > +++ b/drivers/gpu/drm/i915/intel_lvds.c
>> > > @@ -548,7 +548,7 @@ static int intel_lid_notify(struct
notifier_block *nb, unsigned long val,
>> > >         /* Don't force modeset on machines where it
causes a GPU lockup */
>> > >         if (dmi_check_system(intel_no_modeset_on_lid))
>> > >                 goto exit;
>> > > -       if (!acpi_lid_open()) {
>> > > +       if (!val) {
>> > >                 /* do modeset on next lid open event */
>> > >                 dev_priv->modeset_restore =
MODESET_ON_LID_OPEN;
>> > >                 goto exit;
>> > > --
>> > > 2.7.4
>> > >
>> > > --
>> > > To unsubscribe from this list: send the line
"unsubscribe linux-acpi" in
>> > > the body of a message to majordomo at vger.kernel.org
>> > > More majordomo info at 
http://vger.kernel.org/majordomo-info.html
>>  ��칻 �&�~�&� ��+-��ݶ ��w��˛���m�b��Zr����^n�r���z�
��h����&�� �G���h� (�階
>> �ݢj"�� � m�����z�ޖ���f���h���~�m�

Hi, Benjamin
> From: linux-acpi-owner at vger.kernel.org [mailto:linux-acpi-owner at
vger.kernel.org] On Behalf Of Benjamin
> Tissoires
> Subject: Re: [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open()
invocations
> 
> Hi Lv,
> 
> I am trying to reduce the number of parallel discussion we have on the
> same subject, but there is something here I can't let you have.
OK. So let's stop talking in PATCH 4-5.
They are actually cleanups from my point of view.

In fact, I don't see any big conflicts between us.

My point of view is:
There is a gap between (BIOS ensured/Windows expected) acpi control method lid
device behavior and Linux user space expected acpi control method lid device
behavior.
Button driver default behavior should be: button.lid_init_state=ignore
If user space programs have special needs, they can fix problems on their own,
via the following mean:
 echo -n "open" > /sys/modules/button/parameters/lid_init_state
 echo -n "close" > /sys/modules/button/parameters/lid_init_state
Keeping open/close modes is because I don't think there is any bug in button
driver.
So I need to prepare quirk modes from button driver's point of view and use
them as a response to related bug reports reported in acpi community.
Your point of view is:
There is a gap between (BIOS ensured/Windows expected) acpi control method lid
device behavior and Linux user space expected acpi control method lid device
behavior.
Button driver default behavior should be (not 100% sure if this is your
opinion): button.lid_init_state=method
If user space programs have special needs, they can fix them on their own, via
the following mean:
 libinput:name:*Lid Switch*:dmi:*svnMicrosoftCorporation:pnSurface3:*
  LIBINPUT_ATTR_LID_SWITCH_RELIABILITY=write_open
From this point of view, we actually don't need open/close modes.

It seems we just need to determine the following first:
1. Who should be responsible for solving bugs triggered by the conflict between
bios and linux user space expectations:
   button driver? libinput? Some other user space programs? Users?
2. What should be the default button driver behavior?
   button.lid_init_state=ignore? button.lid_init_state=method?
3. If non button driver quirks are working, button driver quirk modes are
useless.
   The question is: Should button.lid_init_state=open/close be kept?
4. From button driver's point of view, button.lid_init_state=ignore seems to
be always correct, so we won't abandon it.
   If we can use libinput to manage platform quirks, then
button.lid_init_state=method also looks useless.
   The question is: Should button.lid_init_state=method be kept?

I should also let you know my preference:
1. using button.lid_init_state=ignore and button.lid_init_state=method as
default behavior is ok for me if answer to 1 is not button driver, otherwise
using button.lid_init_state=method is not ok for me
2. deletion of button.lid_init_state=open/close is ok for me if answer to 1 is
not button driver, otherwise deletion of button.lid_init_state=open/close is not
ok for me
3. deletion of button.lid_init_state=method is always ok for me

See the base line from my side is very clear:
If acpi community need to handle such bug reports, button.lid_init_state=method
cannot be the default behavior.
We are just using a different default behavior than "method" to drive
things to reach the final root caused solution.

Could you let me know your preference so that we can figure out an agreement
between us.
Though I don't know if end users will buy it (they may keep on filing
regression reports in ACPI community).

Can this make the discussion simpler?

So before determining whether we should keep button.lid_init_state=open/close or
not.
We obviously should stop talking here.
You can copy above questions to PATCH 1-2 discussion and reply in order to stop
this.
We can revisit PATCH 4-5 when the basic questions are answered. :)
> 
> On Fri, May 12, 2017 at 8:08 AM, Zheng, Lv <lv.zheng at intel.com>
wrote:
> > Hi,
> >
> > If my previous reply is not persuasive enough.
> > Let me do that in a different way.
> >
> >> From: linux-acpi-owner at vger.kernel.org [mailto:linux-acpi-owner
at vger.kernel.org] On Behalf Of Zheng,
> >> Lv
> >> Subject: RE: [PATCH v2 5/5] ACPI: button: Obselete acpi_lid_open()
invocations
> >>
> >> Hi,
> >>
> >> > From: Benjamin Tissoires [mailto:benjamin.tissoires at
gmail.com]
> >> > Subject: Re: [PATCH v2 5/5] ACPI: button: Obselete
acpi_lid_open() invocations
> >> >
> >> > On Tue, May 9, 2017 at 9:02 AM, Lv Zheng <lv.zheng at
intel.com> wrote:
> >> > > Since notification side has been changed to always
notify kernel listeners
> >> > > using _LID returning value. Now listeners needn't
invoke acpi_lid_open(),
> >> > > it should use a spec suggested control method lid device
usage model:
> >> > > register lid notification and use the notified value
instead, which is the
> >> > > only way to ensure the value is correct for
"button.lid_init_state=ignore"
> >> > > mode or other modes with
"button.lid_fake_events=N" specified.
> >> > >
> >> > > This patch fixes i915 driver to drop acpi_lid_open()
user. It's not
> >> > > possible to change nouveau_connector.c user using a
simple way now. So this
> >> > > patch only marks acpi_lid_open() as deprecated to
accelerate this process
> >> > > by indicating this change to the nouveau developers.
> >> >
> >> > If  the only 2 users of acpi_lid_open() are intel and
nouveau, and if
> >> > they should rely on the value stored in the input node, not
the one
> >> > exported by the _LID method (which can be wrong on some
platforms),
> >> > how about simply changing the implementation of
acpi_lid_open() to
> >> > fetch the value from the input node directly?
> >
> > If acpi_lid_open() returns stored value in input node,
> > then it actually returns the value we notified to the input layer.
> > While i915 and nouveau explicitly do not trust that value and invoke
acpi_lid_open().
> >
> > For button.lid_init_state=method, PATCH 4/5 is useless as the values
are same.
> >
> > However in my reply of PATCH 2.
> > I explained the difference of method/close, for the same reason, we
can also sense the difference of
> method/open.
> > The difference then can explain the usefulness of open/close modes.
> >
> > Given open/close modes are all useful:
> > button.lid_init_state=open
> > 1. button driver sends open to input layer after boot/resume
> > 2. i915/nouveau uses _LID return value after boot/resume
> > If _LID return value after boot/resume is "close", they are
different.
> >
> > button.lid_init_state=close
> > 1. button driver sends close to input layer after boot/resume
> > 2. i915/nouveau uses _LID return value after boot/resume
> > If _LID return value after boot/resume is "open", they are
different.
> >
> > The only way to be consistent to old i915/nouveau behavior is:
> > button.lid_init_state=open/close
> 
> But these two modes are wrong in the absolute case:
> - a laptop has no reasons for not being powered up with the lid
> physically closed (wake on lan?) -> so open is an approximation
> already made on good assumption that there is not a high chance of the
> users powering/resuming the laptop with the lid closed
> - in the "close" case, this setting works for docked laptops, but
if
> the laptop can be docked, it can also be undocked. And if you boot
> with button.lid_init_state=close, undock your laptop, go into suspend,
> resume -> the lid state is now "closed" while it should be
opened.
> 
> So no, these are just workarounds. i915/nouveau expect the acpi/button
> state to be reliable, or they should ignore it. But you can't fake
> events when you are not absolutely sure of what is happening.
> 
> > 1. button driver sends open/close to input layer after boot/resume
> > 2. button driver sends _LID return value to i915 after boot/resume
(PATCH 4)
> > So that i915 can just use the notified value in this patch (PATCH 5).
> > For nouveau, no change has been made for now, and as a concequence,
acpi_lid_open() is still kept
> but marked as deprecated.
> >
> >>
> >> See my reply of PATCH 4.
> >> It seems they trust _LID return value more than what we send to
them.
> >>
> >> We can actually send faked "open/close" to them when
button.lid_init_state=open/close is specified.
> >>
> >> So these 2 patches [PATCH 4-5/5] are used to do a small cleanup
for lid event notifier APIs.
> >> I think they are not strictly related to the lid issues we are
talking about.
> >
> > See Documentation/acpi/acpi-lid.txt:
> > The _LID control method is described to return the "current"
lid state.
> > However the word of "current" has ambiguity, some buggy AML
tables return
> > the lid state upon the last lid notification instead of returning the
lid
> > state upon the last _LID evaluation.
> >
> > In order to have acpi lid event notifier API compliant to the above
mentioned both "buggy" and
> "nonbuggy" implementation.
> > The ensured lid event model interface should be:
> > 1. Lid event notifier listeners invokes acpi_lid_notifier_register().
> > 2. And in the callback, uses _LID return value.
> > This is also the only possible way to combine "receiving lid
notify" and "evaluate _LID" into 1
> single atomic operation.
> >
> > So I trend to remove acpi_lid_open() and enforce the new API.
> >
> > As a conclusion, PATCH 4-5
> > 1. makes a hidden logic explicit - the lid event listeners always use
_LID return value. Less hidden
> logics should leave less chances of bugs.
> > 2. is an implementation for our documented ACPI lid event model.
> > And the implementation is done in a regression safe way.
> 
> I understand all of that. But my point is still that on some
> platforms, the lid acpi state is not reliable, and the code in
> i915/nouveau is not made for those platforms. So the ideal solution is
> to know which platforms are problematic and take the right decisions
> having everything at hands. Just "fixing" the internal API
won't help
> teaching these drivers to not make the assumption that the _LID acpi
> call is always correct.
> 
> So yes, nouveau/i915 might need to be fixed, but IMO, fixing
> acpi/button to report correct (true, accurate, actual, or physical if
> you prefer) is the best, future proof way (minus platform quirks).
This leads to endless discussion.
Let's make agreement on above questions first.

Cheers,
Lv
> 
> Cheers,
> Benjamin
> 
> >
> > Thanks,
> > Lv
> >
> >>
> >> Cheers,
> >> Lv
> >>
> >> >
> >> > Cheers,
> >> > Benjamin
> >> >
> >> > >
> >> > > Cc: <intel-gfx at lists.freedesktop.org>
> >> > > Cc: <nouveau at lists.freedesktop.org>
> >> > > Signed-off-by: Lv Zheng <lv.zheng at intel.com>
> >> > > ---
> >> > >  drivers/acpi/button.c             | 7 ++++++-
> >> > >  drivers/gpu/drm/i915/intel_lvds.c | 2 +-
> >> > >  2 files changed, 7 insertions(+), 2 deletions(-)
> >> > >
> >> > > diff --git a/drivers/acpi/button.c
b/drivers/acpi/button.c
> >> > > index 7ff3a75..50d7898 100644
> >> > > --- a/drivers/acpi/button.c
> >> > > +++ b/drivers/acpi/button.c
> >> > > @@ -348,7 +348,12 @@ int
acpi_lid_notifier_unregister(struct notifier_block *nb)
> >> > >  }
> >> > >  EXPORT_SYMBOL(acpi_lid_notifier_unregister);
> >> > >
> >> > > -int acpi_lid_open(void)
> >> > > +/*
> >> > > + * The intentional usage model is to register a lid
notifier and use the
> >> > > + * notified value instead. Directly evaluating _LID
without seeing a
> >> > > + * Notify(lid, 0x80) is not reliable.
> >> > > + */
> >> > > +int __deprecated acpi_lid_open(void)
> >> > >  {
> >> > >         if (!lid_device)
> >> > >                 return -ENODEV;
> >> > > diff --git a/drivers/gpu/drm/i915/intel_lvds.c
b/drivers/gpu/drm/i915/intel_lvds.c
> >> > > index 9ca4dc4..8ca9080 100644
> >> > > --- a/drivers/gpu/drm/i915/intel_lvds.c
> >> > > +++ b/drivers/gpu/drm/i915/intel_lvds.c
> >> > > @@ -548,7 +548,7 @@ static int intel_lid_notify(struct
notifier_block *nb, unsigned long val,
> >> > >         /* Don't force modeset on machines where it
causes a GPU lockup */
> >> > >         if (dmi_check_system(intel_no_modeset_on_lid))
> >> > >                 goto exit;
> >> > > -       if (!acpi_lid_open()) {
> >> > > +       if (!val) {
> >> > >                 /* do modeset on next lid open event */
> >> > >                 dev_priv->modeset_restore =
MODESET_ON_LID_OPEN;
> >> > >                 goto exit;
> >> > > --
> >> > > 2.7.4
> >> > >
> >> > > --
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