Re: [PATCH v7 1/2] ACPI / button: Fix an issue that the platform triggered reliable events may not be delivered to the userspace

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, July 26, 2016 05:52:24 PM Lv Zheng wrote:
> On most platforms, _LID returning value, lid open/close events are all
> reliable, but there are exceptions. Some AML tables report wrong initial
> lid state (Link 1), and some of them never report lid open state (Link 2).
> The usage model on such buggy platforms is:
> 1. The initial lid state returned from _LID is not reliable;
> 2. The lid open event is not reliable;
> 3. The lid close event is always reliable, used by the platform firmware to
>    trigger OSPM power saving operations.
> This usage model is not compliant to the Linux SW_LID model as the Linux
> userspace is very strict to the reliability of the open events.
> 
> In order not to trigger issues on such buggy platforms, the ACPI button
> driver currently implements a lid_init_state=open quirk to send additional
> "open" event after resuming. However, this is still not sufficient because:
> 1. Some special usage models (e.x., the dark resume scenario) cannot be
>    supported by this mode.
> 2. If a "close" event is not used to trigger "suspend", then the subsequent
>    "close" events cannot be seen by the userspace.
> So we need to stop sending the additional "open" event and switch the
> driver to lid_init_state=ignore mode and make sure the platform triggered
> events can be reliably delivered to the userspace. The userspace programs
> then can be changed to not to be strict to the "open" events on such buggy
> platforms.
> 
> Why will the subsequent "close" events be lost? This is because the input
> layer automatically filters redundant events for switch events. Thus given
> that the buggy AML tables do not guarantee paired "open"/"close" events,
> the ACPI button driver currently is not able to guarantee that the platform
> triggered reliable events can be always be seen by the userspace via
> SW_LID.
> 
> This patch adds a mechanism to insert lid events as a compensation for the
> platform triggered ones to form a complete event switches in order to make
> sure that the platform triggered events can always be reliably delivered
> to the userspace. This essentially guarantees that the platform triggered
> reliable "close" events will always be relibly delivered to the userspace.
> 
> However this mechanism is not suitable for lid_init_state=open/method as
> it should not send the complement switch event for the unreliable initial
> lid state notification. 2 unreliable events can trigger unexpected
> behavior. Thus this patch only implements this mechanism for
> lid_init_state=ignore.
> 
> Link 1: https://bugzilla.kernel.org/show_bug.cgi?id=89211
>         https://bugzilla.kernel.org/show_bug.cgi?id=106151
> Link 2: https://bugzilla.kernel.org/show_bug.cgi?id=106941
> Signed-off-by: Lv Zheng <lv.zheng@intel.com>
> Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Cc: Benjamin Tissoires <benjamin.tissoires@gmail.com>
> Cc: Bastien Nocera: <hadess@hadess.net>
> Cc: linux-input@vger.kernel.org
> ---
>  drivers/acpi/button.c |   51 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
> index 148f4e5..dca1806 100644
> --- a/drivers/acpi/button.c
> +++ b/drivers/acpi/button.c
> @@ -19,6 +19,8 @@
>   * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   */
>  
> +#define pr_fmt(fmt) "ACPI : button: " fmt
> +
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
> @@ -104,6 +106,8 @@ struct acpi_button {
>  	struct input_dev *input;
>  	char phys[32];			/* for input device */
>  	unsigned long pushed;
> +	int last_state;
> +	unsigned long last_time;

Why don't you use ktime_t here?

>  	bool suspended;
>  };
>  
> @@ -111,6 +115,10 @@ static BLOCKING_NOTIFIER_HEAD(acpi_lid_notifier);
>  static struct acpi_device *lid_device;
>  static u8 lid_init_state = ACPI_BUTTON_LID_INIT_METHOD;
>  
> +static unsigned long lid_report_interval __read_mostly = 500;
> +module_param(lid_report_interval, ulong, 0644);
> +MODULE_PARM_DESC(lid_report_interval, "Interval (ms) between lid key events");
> +
>  /* --------------------------------------------------------------------------
>                                FS Interface (/proc)
>     -------------------------------------------------------------------------- */
> @@ -135,9 +143,48 @@ static int acpi_lid_notify_state(struct acpi_device *device, int state)
>  	struct acpi_button *button = acpi_driver_data(device);
>  	int ret;
>  
> -	/* input layer checks if event is redundant */
> +	if (button->last_state == !!state &&
> +	    time_after(jiffies, button->last_time +
> +				msecs_to_jiffies(lid_report_interval))) {

And ktime_after() here?

> +		/* Complain the buggy firmware */
> +		pr_warn_once("The lid device is not compliant to SW_LID.\n");
> +
> +		/*
> +		 * Send the unreliable complement switch event:
> +		 *
> +		 * On most platforms, the lid device is reliable. However
> +		 * there are exceptions:
> +		 * 1. Platforms returning initial lid state as "close" by
> +		 *    default after booting/resuming:
> +		 *     https://bugzilla.kernel.org/show_bug.cgi?id=89211
> +		 *     https://bugzilla.kernel.org/show_bug.cgi?id=106151
> +		 * 2. Platforms never reporting "open" events:
> +		 *     https://bugzilla.kernel.org/show_bug.cgi?id=106941
> +		 * On these buggy platforms, the usage model of the ACPI
> +		 * lid device actually is:
> +		 * 1. The initial returning value of _LID may not be
> +		 *    reliable.
> +		 * 2. The open event may not be reliable.
> +		 * 3. The close event is reliable.
> +		 *
> +		 * But SW_LID is typed as input switch event, the input
> +		 * layer checks if the event is redundant. Hence if the
> +		 * state is not switched, the userspace cannot see this
> +		 * platform triggered reliable event. By inserting a
> +		 * complement switch event, it then is guaranteed that the
> +		 * platform triggered reliable one can always be seen by
> +		 * the userspace.
> +		 */
> +		if (lid_init_state == ACPI_BUTTON_LID_INIT_IGNORE) {
> +			input_report_switch(button->input, SW_LID, state);
> +			input_sync(button->input);
> +		}
> +	}
> +	/* Send the platform triggered reliable event */
>  	input_report_switch(button->input, SW_LID, !state);
>  	input_sync(button->input);
> +	button->last_state = !!state;
> +	button->last_time = jiffies;

And ktime_get() here?

>  
>  	if (state)
>  		pm_wakeup_event(&device->dev, 0);
> @@ -407,6 +454,8 @@ static int acpi_button_add(struct acpi_device *device)
>  		strcpy(name, ACPI_BUTTON_DEVICE_NAME_LID);
>  		sprintf(class, "%s/%s",
>  			ACPI_BUTTON_CLASS, ACPI_BUTTON_SUBCLASS_LID);
> +		button->last_state = !!acpi_lid_evaluate_state(device);
> +		button->last_time = jiffies;

And here?

>  	} else {
>  		printk(KERN_ERR PREFIX "Unsupported hid [%s]\n", hid);
>  		error = -ENODEV;
> 

Thanks,
Rafael