Date:	Thu, 19 May 2016 00:56:35 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	"Zheng, Lv" <lv.zheng@...el.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"Bastien Nocera:" <hadess@...ess.net>
Subject: Re: [RFC PATCH 1/2] ACPI / button: Send "open" state after boot/resume

On Wed, May 18, 2016 at 3:25 AM, Zheng, Lv <lv.zheng@...el.com> wrote:
> Hi, Rafael
>
> Thanks for the review.
>
>> From: rjwysocki@...il.com [mailto:rjwysocki@...il.com] On Behalf Of
>> Rafael J. Wysocki
>> Sent: Wednesday, May 18, 2016 7:37 AM
>> To: Zheng, Lv <lv.zheng@...el.com>
>> Cc: Wysocki, Rafael J <rafael.j.wysocki@...el.com>; Rafael J. Wysocki
>> <rjw@...ysocki.net>; Brown, Len <len.brown@...el.com>; Lv Zheng
>> <zetalog@...il.com>; Linux Kernel Mailing List <linux-
>> kernel@...r.kernel.org>; ACPI Devel Maling List <linux-acpi@...r.kernel.org>;
>> Bastien Nocera: <hadess@...ess.net>
>> Subject: Re: [RFC PATCH 1/2] ACPI / button: Send "open" state after
>> boot/resume
>>
>> On Tue, May 17, 2016 at 10:27 AM, Lv Zheng <lv.zheng@...el.com> wrote:
>> > (This patch hasn't been tested, it's sent for comments)
>>
>> I have a couple of concerns (see below).
>>
>> > Linux userspace (systemd-logind) keeps on rechecking lid state when the
>> > lid state is closed. If it failed to update the lid state to open after
>> > boot/resume, it could suspend the system. But as:
>> > 1. Traditional ACPI platform may not generate the lid open event after
>> >    resuming as the open event is actually handled by the BIOS and the system
>> >    is then resumed from a FACS vector.
>> > 2. The _LID control method's initial returning value is not reliable. The
>> >    _LID control method is described to return the "current" lid state,
>> >    however the word of "current" has ambiguity, many BIOSen return lid
>> >    state upon last lid notification while the developers may think the
>> >    BIOSen should always return the lid state upon last _LID evaluation.
>> >    There won't be difference when we evaluate _LID during the runtime, the
>> >    problem is the initial returning value of this function. When the BIOSen
>> >    implement this control method with cached value, the initial returning
>> >    value is likely not reliable.
>> > Thus there is no mean for the ACPI lid driver to provide such an event
>> > conveying correct current lid state. When there is no such an event or the
>> > event conveys wrong result, false suspending can be examined.
>> >
>> > The root cause of the issue is systemd itself, it could handle the ACPI
>> > control method lid device by implementing a special option like
>> > LidSwitchLevelTriggered=False when it detected the ACPI lid device. However
>> > there is no explicit documentation clarified the ambiguity, we need to
>> > work it around in the kernel before systemd changing its mind.
>>
>> The above doesn't explain how the issue is addressed here.
> [Lv Zheng]
> The story is a bit long.
> We can see several issues that some platform suspends right after boot/resume.
> We noticed that on that platforms, _LID is always implemented with cached lid state returned.
> And it's initial returning value may be "closed" after boot/resume.
>
> It appears the acpi_lid_send_state() sent after boot/resume is the culprit to report the wrong lid state to the userspace.
> But to our surprise, after delete the 2 lines, reporters still can see suspends after boot/resume.
> That's because of systemd implementation.
> It contains code logic that:
> When the lid state is closed, a re-checking mechanism is installed.
> So if we do not send any notification after boot/resume and the old lid state is "closed".
> systemd determines to suspend in the re-checking mechanism.

If that really is the case, it is plain silly and I don't think we can
do anything in the kernel to help here.

>>
>> > Link 1: https://lkml.org/2016/3/7/460
>> > Link 2: https://github.com/systemd/systemd/issues/2087
>> > Link 3: https://bugzilla.kernel.org/show_bug.cgi?id=89211
>> >         https://bugzilla.kernel.org/show_bug.cgi?id=106151
>> >         https://bugzilla.kernel.org/show_bug.cgi?id=106941
>> > Signed-off-by: Lv Zheng <lv.zheng@...el.com>
>> > Cc: Bastien Nocera: <hadess@...ess.net>
>> > ---
>> >  drivers/acpi/button.c |   63
>> +++++++++++++++++++++++++++++++++++++++++++++----
>> >  1 file changed, 59 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
>> > index 5c3b091..bb14ca5 100644
>> > --- a/drivers/acpi/button.c
>> > +++ b/drivers/acpi/button.c
>> > @@ -53,6 +53,10 @@
>> >  #define ACPI_BUTTON_DEVICE_NAME_LID    "Lid Switch"
>> >  #define ACPI_BUTTON_TYPE_LID           0x05
>> >
>> > +#define ACPI_BUTTON_LID_INIT_IGNORE    0x00
>> > +#define ACPI_BUTTON_LID_INIT_OPEN      0x01
>> > +#define ACPI_BUTTON_LID_INIT_METHOD    0x02
>> > +
>> >  #define _COMPONENT             ACPI_BUTTON_COMPONENT
>> >  ACPI_MODULE_NAME("button");
>> >
>> > @@ -105,6 +109,7 @@ struct acpi_button {
>> >
>> >  static BLOCKING_NOTIFIER_HEAD(acpi_lid_notifier);
>> >  static struct acpi_device *lid_device;
>> > +static u8 lid_init_state = ACPI_BUTTON_LID_INIT_OPEN;
>> >
>> >  /* --------------------------------------------------------------------------
>> >                                FS Interface (/proc)
>> > @@ -246,7 +251,8 @@ int acpi_lid_open(void)
>> >  }
>> >  EXPORT_SYMBOL(acpi_lid_open);
>> >
>> > -static int acpi_lid_send_state(struct acpi_device *device)
>> > +static int acpi_lid_send_state(struct acpi_device *device,
>> > +                              bool notify_init_state)
>> >  {
>> >         struct acpi_button *button = acpi_driver_data(device);
>> >         unsigned long long state;
>> > @@ -257,6 +263,10 @@ static int acpi_lid_send_state(struct acpi_device
>> *device)
>> >         if (ACPI_FAILURE(status))
>> >                 return -ENODEV;
>> >
>> > +       if (notify_init_state &&
>> > +           lid_init_state == ACPI_BUTTON_LID_INIT_OPEN)
>> > +               state = 1;
>> > +
>>
>> Why do we need to complicate this function?
>>
>> Can't we have a separate function for sending the fake "lid open" event?
> [Lv Zheng]
>
> Yes, we can.
> But I put the code here for reasons.
>
> I intentionally kept the _LID evaluation right after boot/resume.
> Because I validated Windows behavior.
> It seems Windows evaluates _LID right after boot.
> So I kept _LID evaluated right after boot to prevent compliance issues.

I don't quite see what compliance issues could result from skipping
the _LID evaluation after boot.

>>
>> >         /* input layer checks if event is redundant */
>> >         input_report_switch(button->input, SW_LID, !state);
>> >         input_sync(button->input);
>> > @@ -278,6 +288,13 @@ static int acpi_lid_send_state(struct acpi_device
>> *device)
>> >         return ret;
>> >  }
>> >
>> > +static int acpi_lid_send_init_state(struct acpi_device *device)
>> > +{
>> > +       if (lid_init_state != ACPI_BUTTON_LID_INIT_IGNORE)
>> > +               return acpi_lid_send_state(device, true);
>> > +       return 0;
>> > +}
>> > +
>> >  static void acpi_button_notify(struct acpi_device *device, u32 event)
>> >  {
>> >         struct acpi_button *button = acpi_driver_data(device);
>> > @@ -290,7 +307,7 @@ static void acpi_button_notify(struct acpi_device
>> *device, u32 event)
>> >         case ACPI_BUTTON_NOTIFY_STATUS:
>> >                 input = button->input;
>> >                 if (button->type == ACPI_BUTTON_TYPE_LID) {
>> > -                       acpi_lid_send_state(device);
>> > +                       acpi_lid_send_state(device, false);
>>
>> I wouldn't change this code at all.
>>
>> >                 } else {
>> >                         int keycode;
>> >
>> > @@ -335,7 +352,7 @@ static int acpi_button_resume(struct device *dev)
>> >
>> >         button->suspended = false;
>> >         if (button->type == ACPI_BUTTON_TYPE_LID)
>> > -               return acpi_lid_send_state(device);
>> > +               return acpi_lid_send_init_state(device);
>> >         return 0;
>> >  }
>> >  #endif
>> > @@ -416,7 +433,7 @@ static int acpi_button_add(struct acpi_device *device)
>> >         if (error)
>> >                 goto err_remove_fs;
>> >         if (button->type == ACPI_BUTTON_TYPE_LID) {
>> > -               acpi_lid_send_state(device);
>> > +               acpi_lid_send_init_state(device);
>> >                 /*
>> >                  * This assumes there's only one lid device, or if there are
>> >                  * more we only care about the last one...
>> > @@ -446,4 +463,42 @@ static int acpi_button_remove(struct acpi_device
>> *device)
>> >         return 0;
>> >  }
>> >
>> > +static int param_set_lid_init_state(const char *val, struct kernel_param *kp)
>> > +{
>> > +       int result = 0;
>> > +
>> > +       if (!strncmp(val, "open", sizeof("open") - 1)) {
>> > +               lid_init_state = ACPI_BUTTON_LID_INIT_OPEN;
>> > +               pr_info("Notify initial lid state as open\n");
>> > +       } else if (!strncmp(val, "method", sizeof("method") - 1)) {
>> > +               lid_init_state = ACPI_BUTTON_LID_INIT_METHOD;
>> > +               pr_info("Notify initial lid state with _LID return value\n");
>> > +       } else if (!strncmp(val, "ignore", sizeof("ignore") - 1)) {
>> > +               lid_init_state = ACPI_BUTTON_LID_INIT_IGNORE;
>> > +               pr_info("Do not notify initial lid state\n");
>> > +       } else
>> > +               result = -EINVAL;
>> > +       return result;
>> > +}
>> > +
>> > +static int param_get_lid_init_state(char *buffer, struct kernel_param *kp)
>> > +{
>> > +       switch (lid_init_state) {
>> > +       case ACPI_BUTTON_LID_INIT_OPEN:
>> > +               return sprintf(buffer, "open");
>> > +       case ACPI_BUTTON_LID_INIT_METHOD:
>> > +               return sprintf(buffer, "method");
>> > +       case ACPI_BUTTON_LID_INIT_IGNORE:
>> > +               return sprintf(buffer, "ignore");
>> > +       default:
>> > +               return sprintf(buffer, "invalid");
>> > +       }
>> > +       return 0;
>> > +}
>> > +
>> > +module_param_call(lid_init_state,
>> > +                 param_set_lid_init_state, param_get_lid_init_state,
>> > +                 NULL, 0644);
>> > +MODULE_PARM_DESC(lid_init_state, "Behavior for reporting LID initial
>> state");
>> > +
>>
>> I'm not seeing a particular value in having this command line switch
>> to be honest.  Apparently, the issue can be worked around from user
>> space in any case, so why do we need one more way to work around it?
>>
>> >  module_acpi_driver(acpi_button_driver);
>> > --
>>
>> The main concern is general, though.  Evidently, we send fake lid
>> input events to user space on init and resume.  I don't think this is
>> a good idea, because it may confuse systems like Chrome that want to
>> implement "dark resume" scenarios and may rely on input events to
>> decide whether to start a UI or suspend again.
>>
>> Thus it might be better to simply drop the sending of those fake input
>> events from the code.
> [Lv Zheng]
> If we did this right now, many other userspace could be broken.
> So we prepared the options to allow users to choose.

Do we have any evidence that any other user space stacks are affected?

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