[PATCH v2] input: API for Setting a Timestamp from a Driver

Atif Niyaz
2019-07-18T19:41:42Z

Currently, evdev stamps events with timestamps acquired in evdev_events.
However, this timestamping may not be accurate in terms of measuring
when the actual event happened. This API allows any 3rd party driver to
be able to call input_set_timestamp, and provide a timestamp that can be
utilized in order to provide a more accurate sense of time for the
event

Signed-off-by: Atif Niyaz <atifniyaz@google.com>
---
drivers/input/evdev.c | 43 +++++++++++++++++--------------------------
drivers/input/input.c | 16 ++++++++++++++++
include/linux/input.h | 37 +++++++++++++++++++++++++++++++++++++
3 files changed, 70 insertions(+), 26 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 867c2cfd0038..3160b2223955 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -25,13 +25,6 @@
#include <linux/cdev.h>
#include "input-compat.h"

-enum evdev_clock_type {
- EV_CLK_REAL = 0,
- EV_CLK_MONO,
- EV_CLK_BOOT,
- EV_CLK_MAX
-};
-
struct evdev {
int open;
struct input_handle handle;
@@ -53,7 +46,7 @@ struct evdev_client {
struct fasync_struct *fasync;
struct evdev *evdev;
struct list_head node;
- unsigned int clk_type;
+ enum input_clock_type clk_type;
bool revoked;
unsigned long *evmasks[EV_CNT];
unsigned int bufsize;
@@ -150,16 +143,19 @@ static void __evdev_flush_queue(struct evdev_client *client, unsigned int type)
static void __evdev_queue_syn_dropped(struct evdev_client *client)
{
struct input_event ev;
- ktime_t time;
struct timespec64 ts;
+ ktime_t *time = input_get_timestamp(client->evdev->handle.dev);

- time = client->clk_type == EV_CLK_REAL ?
- ktime_get_real() :
- client->clk_type == EV_CLK_MONO ?
- ktime_get() :
- ktime_get_boottime();
+ switch (client->clk_type) {
+ case INPUT_CLK_REAL:
+ case INPUT_CLK_MONO:
+ ts = ktime_to_timespec64(time[client->clk_type]);
+ break;
+ default:
+ ts = ktime_to_timespec64(time[INPUT_CLK_BOOT]);
+ break;
+ }

- ts = ktime_to_timespec64(time);
ev.input_event_sec = ts.tv_sec;
ev.input_event_usec = ts.tv_nsec / NSEC_PER_USEC;
ev.type = EV_SYN;
@@ -185,21 +181,21 @@ static void evdev_queue_syn_dropped(struct evdev_client *client)
spin_unlock_irqrestore(&client->buffer_lock, flags);
}

-static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
+static int evdev_set_clk_type(struct evdev_client *client, clockid_t clkid)
{
unsigned long flags;
- unsigned int clk_type;
+ enum input_clock_type clk_type;

switch (clkid) {

case CLOCK_REALTIME:
- clk_type = EV_CLK_REAL;
+ clk_type = INPUT_CLK_REAL;
break;
case CLOCK_MONOTONIC:
- clk_type = EV_CLK_MONO;
+ clk_type = INPUT_CLK_MONO;
break;
case CLOCK_BOOTTIME:
- clk_type = EV_CLK_BOOT;
+ clk_type = INPUT_CLK_BOOT;
break;
default:
return -EINVAL;
@@ -307,12 +303,7 @@ static void evdev_events(struct input_handle *handle,
{
struct evdev *evdev = handle->private;
struct evdev_client *client;
- ktime_t ev_time[EV_CLK_MAX];
-
- ev_time[EV_CLK_MONO] = ktime_get();
- ev_time[EV_CLK_REAL] = ktime_mono_to_real(ev_time[EV_CLK_MONO]);
- ev_time[EV_CLK_BOOT] = ktime_mono_to_any(ev_time[EV_CLK_MONO],
- TK_OFFS_BOOT);
+ ktime_t *ev_time = input_get_timestamp(handle->dev);

rcu_read_lock();

diff --git a/drivers/input/input.c b/drivers/input/input.c
index 7f3c5fcb9ed6..b8d711980bdd 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -1894,6 +1894,22 @@ void input_free_device(struct input_dev *dev)
}
EXPORT_SYMBOL(input_free_device);

+/**
+ * input_get_timestamp - get timestamp for input events
+ * @dev: input device to get timestamp from
+ *
+ * A valid timestamp is a timestamp of non-zero value.
+ */
+ktime_t *input_get_timestamp(struct input_dev *dev)
+{
+ const ktime_t invalid_timestamp = ktime_set(0, 0);
+
+ if (!ktime_compare(dev->timestamp[INPUT_CLK_MONO], invalid_timestamp))
+ input_set_timestamp(dev, ktime_get());
+ return dev->timestamp;
+}
+EXPORT_SYMBOL(input_get_timestamp);
+
/**
* input_set_capability - mark device as capable of a certain event
* @dev: device that is capable of emitting or accepting event
diff --git a/include/linux/input.h b/include/linux/input.h
index 510e78558c10..cf8c69abb342 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -33,6 +33,13 @@ struct input_value {
__s32 value;
};

+enum input_clock_type {
+ INPUT_CLK_REAL = 0,
+ INPUT_CLK_MONO,
+ INPUT_CLK_BOOT,
+ INPUT_CLK_MAX
+};
+
/**
* struct input_dev - represents an input device
* @name: name of the device
@@ -114,6 +121,8 @@ struct input_value {
* @vals: array of values queued in the current frame
* @devres_managed: indicates that devices is managed with devres framework
* and needs not be explicitly unregistered or freed.
+ * @timestamp: storage for a timestamp set by input_set_timestamp called
+ * by a driver
*/
struct input_dev {
const char *name;
@@ -184,6 +193,8 @@ struct input_dev {
struct input_value *vals;

bool devres_managed;
+
+ ktime_t timestamp[INPUT_CLK_MAX];
};
#define to_input_dev(d) container_of(d, struct input_dev, dev)

@@ -382,6 +393,32 @@ void input_close_device(struct input_handle *);

int input_flush_device(struct input_handle *handle, struct file *file);

+/**
+ * input_set_timestamp - set timestamp for input events
+ * @dev: input device to set timestamp for
+ * @timestamp: the time at which the event has occurred
+ * in CLOCK_MONOTONIC
+ *
+ * This function is intended to provide to the input system a more
+ * accurate time of when an event actually occurred. The driver should
+ * call this function as soon as a timestamp is acquired ensuring
+ * clock conversions in input_set_timestamp are done correctly.
+ *
+ * The system entering a suspend between timestamp acquisition and
+ * calling input_set_timestamp can result in inaccurate conversions.
+ *
+ */
+static inline void input_set_timestamp(struct input_dev *dev,
+ ktime_t timestamp)
+{
+ dev->timestamp[INPUT_CLK_MONO] = timestamp;
+ dev->timestamp[INPUT_CLK_REAL] = ktime_mono_to_real(timestamp);
+ dev->timestamp[INPUT_CLK_BOOT] = ktime_mono_to_any(
+ timestamp, TK_OFFS_BOOT);
+}
+
+ktime_t *input_get_timestamp(struct input_dev *dev);
+
void input_event(struct input_dev *dev, unsigned int type, unsigned int code, int value);
void input_inject_event(struct input_handle *handle, unsigned int type, unsigned int code, int value);

--
2.22.0.510.g264f2c817a-goog