[PATCH 1/2] Input: Add "inhibited" property

Andrzej Pietrasiewicz
2020-04-30T16:16:52Z

From: Patrik Fimml <patrikf@chromium.org>

Userspace might want to implement a policy to temporarily disregard input
from certain devices, including not treating them as wakeup sources.

An example use case is a laptop, whose keyboard can be folded under the
screen to create tablet-like experience. The user then must hold the laptop
in such a way that it is difficult to avoid pressing the keyboard keys. It
is therefore desirable to temporarily disregard input from the keyboard,
until it is folded back. This obviously is a policy which should be kept
out of the kernel, but the kernel must provide suitable means to implement
such a policy.

This patch adds a sysfs interface for exactly this purpose.

To implement the said interface it adds an "inhibited" property to struct
input_dev and two optional methods - inhibit() and uninhibit(), and
effectively creates four states a device can be in: closed uninhibited,
closed inhibited, open uninhibited, open inhibited. It also defers calling
driver's ->open() and ->close() to until they are actually needed, e.g. it
makes no sense to prepare the underlying device for generating events
(->open()) if the device is inhibited.

uninhibit
closed <------------ closed
uninhibited ------------> inhibited
| ^ inhibit | ^
1st | | 1st | |
open | | open | |
| | | |
| | last | | last
| | close | | close
v | uninhibit v |
open <------------ open
uninhibited ------------> inhibited

The top inhibit/uninhibit transition happens when users == 0.
The bottom inhibit/uninhibit transition happens when users > 0.
The left open/close transition happens when !inhibited.
The right open/close transition happens when inhibited.
Due to all transitions being serialized with dev->mutex, it is impossible
to have "diagonal" transitions between closed uninhibited and open
inhibited or between open uninhibited and closed inhibited.

While open()/close() could be used in place of uninhibit()/inhibit(),
underlying driver implementations have very different ideas of what it
means to open/close, to suspend/resume or to pm runtime suspend/resume.
On top of that close() does not return a code, so using close() there be
no way to actually fail inhibiting.

It is drivers' responsibility to implement their inhibiting capability in
terms of whatever is suitable in their context, be it open/close,
inhibit/uninhibit or a combination of both. The drivers should also ensure
that they properly interact with suspend/resume and PM runtime, because
most likely a side effect of inhibiting a device should be its going into
low power mode. Properly inhibiting a device means to prevent it from being
a wakeup source, so drivers should also take care of that.

Signed-off-by: Patrik Fimml <patrikf@chromium.org>
Co-developed-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
---
drivers/input/input.c | 134 +++++++++++++++++++++++++++++++++++++++---
include/linux/input.h | 8 +++
2 files changed, 133 insertions(+), 9 deletions(-)

diff --git a/drivers/input/input.c b/drivers/input/input.c
index 3cfd2c18eebd..ee1d17b23b54 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -367,8 +367,13 @@ static int input_get_disposition(struct input_dev *dev,
static void input_handle_event(struct input_dev *dev,
unsigned int type, unsigned int code, int value)
{
- int disposition = input_get_disposition(dev, type, code, &value);
+ int disposition;

+ /* filter-out events from inhibited devices */
+ if (dev->inhibited)
+ return;
+
+ disposition = input_get_disposition(dev, type, code, &value);
if (disposition != INPUT_IGNORE_EVENT && type != EV_SYN)
add_input_randomness(type, code, value);

@@ -612,7 +617,7 @@ int input_open_device(struct input_handle *handle)

handle->open++;

- if (dev->users++) {
+ if (dev->users++ || dev->inhibited) {
/*
* Device is already opened, so we can exit immediately and
* report success.
@@ -660,6 +665,14 @@ int input_flush_device(struct input_handle *handle, struct file *file)
}
EXPORT_SYMBOL(input_flush_device);

+static inline void input_stop(struct input_dev *dev)
+{
+ if (dev->poller)
+ input_dev_poller_stop(dev->poller);
+ if (dev->close)
+ dev->close(dev);
+}
+
/**
* input_close_device - close input device
* @handle: handle through which device is being accessed
@@ -675,13 +688,8 @@ void input_close_device(struct input_handle *handle)

__input_release_device(handle);

- if (!--dev->users) {
- if (dev->poller)
- input_dev_poller_stop(dev->poller);
-
- if (dev->close)
- dev->close(dev);
- }
+ if (!dev->inhibited && !--dev->users)
+ input_stop(dev);

if (!--handle->open) {
/*
@@ -1416,12 +1424,49 @@ static ssize_t input_dev_show_properties(struct device *dev,
}
static DEVICE_ATTR(properties, S_IRUGO, input_dev_show_properties, NULL);

+static int input_inhibit(struct input_dev *dev);
+static int input_uninhibit(struct input_dev *dev);
+
+static ssize_t inhibited_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct input_dev *input_dev = to_input_dev(dev);
+
+ return scnprintf(buf, PAGE_SIZE, "%d\n", input_dev->inhibited);
+}
+
+static ssize_t inhibited_store(struct device *dev,
+ struct device_attribute *attr, const char *buf,
+ size_t len)
+{
+ struct input_dev *input_dev = to_input_dev(dev);
+ ssize_t rv;
+ bool inhibited;
+
+ if (strtobool(buf, &inhibited))
+ return -EINVAL;
+
+ if (inhibited)
+ rv = input_inhibit(input_dev);
+ else
+ rv = input_uninhibit(input_dev);
+
+ if (rv != 0)
+ return rv;
+
+ return len;
+}
+
+static DEVICE_ATTR_RW(inhibited);
+
static struct attribute *input_dev_attrs[] = {
&dev_attr_name.attr,
&dev_attr_phys.attr,
&dev_attr_uniq.attr,
&dev_attr_modalias.attr,
&dev_attr_properties.attr,
+ &dev_attr_inhibited.attr,
NULL
};

@@ -1703,6 +1748,77 @@ void input_reset_device(struct input_dev *dev)
}
EXPORT_SYMBOL(input_reset_device);

+static int input_inhibit(struct input_dev *dev)
+{
+ int ret = 0;
+
+ mutex_lock(&dev->mutex);
+
+ if (dev->inhibited)
+ goto out;
+
+ if (dev->users) {
+ if (dev->inhibit) {
+ ret = dev->inhibit(dev);
+ if (ret)
+ goto out;
+ }
+ input_stop(dev);
+ }
+
+ spin_lock_irq(&dev->event_lock);
+ input_dev_release_keys(dev);
+ input_dev_toggle(dev, false);
+ spin_unlock_irq(&dev->event_lock);
+
+ dev->inhibited = true;
+
+out:
+ mutex_unlock(&dev->mutex);
+ return ret;
+}
+
+static int input_uninhibit(struct input_dev *dev)
+{
+ int ret = 0;
+
+ mutex_lock(&dev->mutex);
+
+ if (!dev->inhibited)
+ goto out;
+
+ if (dev->users) {
+ if (dev->open) {
+ ret = dev->open(dev);
+ if (ret)
+ goto toggle;
+ }
+ if (dev->uninhibit) {
+ ret = dev->uninhibit(dev);
+ if (ret) {
+ if (dev->close)
+ dev->close(dev);
+ goto toggle;
+ }
+ }
+ if (dev->poller)
+ input_dev_poller_start(dev->poller);
+ }
+
+ dev->inhibited = false;
+
+toggle:
+ if (!dev->inhibited) {
+ spin_lock_irq(&dev->event_lock);
+ input_dev_toggle(dev, true);
+ spin_unlock_irq(&dev->event_lock);
+ }
+
+out:
+ mutex_unlock(&dev->mutex);
+ return ret;
+}
+
#ifdef CONFIG_PM_SLEEP
static int input_dev_suspend(struct device *dev)
{
diff --git a/include/linux/input.h b/include/linux/input.h
index 56f2fd32e609..a15839e3b808 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -127,6 +127,9 @@ enum input_clock_type {
* and needs not be explicitly unregistered or freed.
* @timestamp: storage for a timestamp set by input_set_timestamp called
* by a driver
+ * @inhibit: makes the device ignore all input
+ * @uninhibit: undoes the effect of inhibit
+ * @inhibited: indicates that the input device is inhibited
*/
struct input_dev {
const char *name;
@@ -201,6 +204,11 @@ struct input_dev {
bool devres_managed;

ktime_t timestamp[INPUT_CLK_MAX];
+
+ int (*inhibit)(struct input_dev *dev);
+ int (*uninhibit)(struct input_dev *dev);
+
+ bool inhibited;
};
#define to_input_dev(d) container_of(d, struct input_dev, dev)

--
2.17.1