Re: Re: [PATCH] Introduce Naming Convention in Input Subsystem

[Aniroop Mathur <a.mathur@samsung.com>]

Hello Mr. Torokhov,
Greetings!

On Thu, Jan 09, 2014 at 10:27:56AM +0530, Aniroop Mathur wrote:
> This patch allows user(driver) to set sysfs node name of input
> devices.  To set sysfs node name, user(driver) just needs to set
> node_name_unique variable.  If node_name_unique is not set, default
> name is given(as before).  So, this patch is completely
> backward-compatible.
> 
> Sysfs Input node name format is: input_
> Sysfs Event node name format is: event_
>
> This "name" is given by user and automatically, prefix(input and
> event) is added by input core.
> 
> This name must be unique among all input devices and driver(user) has
> the responsibility to ensure it.  If same name is used again for other
> input device, registration of that input device will fail because two
> input devices cannot have same name.
> 
> Advantages of this patch are:
> 
> 1. Reduces Booting Time of HAL/Upper-Layer because now HAL or
> Upper-Layer do not need to search input/event number corresponding to
> each input device in /dev/input/...  This searching in /dev/input/ was
> taking too much time.  (Especially in mobile devices, where there are
> many input devices (many sensors, touchscreen, etc), it reduces a lot
> of booting time)

I am sorry, how much time does it take to scan a directory of what, 20
devices? If it such a factor have udev create nodes that are easier for
you to locate, similarly how we already create nodes by-id and by-path.
For example you can encode major:minor in device name.

Re: (Aniroop Mathur)
Its correct that we can set name of a device node using udev. 
Yes, this will change the name of device node(/dev/...) but not sysfs node.(/sys/class/input/...)
So now, the problem area will shift from dev path to sysfs path, 
because now we dont know which sysfs node to refer for a particular input device
and hence HAL/Upper-Layer will need to search in /sys/class/input/... instead of /dev/... directory.

Moreover, as i know, udev is mainly for hot-pluggable devices, but my problem is for platform devices,
which are already present on the board during boot up. (Like in Embedded devices)

To avoid confusion and make the problem more clear, 
I would like to explain the problem and my suggestion by taking an example:

Suppose in a mobile device, there are 10 embedded input devices as below:
Proximity ---                /dev/input0  --- /sys/class/input/input0 --- /sys/class/input/event0
Magnetometer ---      /dev/input1   --- /sys/class/input/input1 --- /sys/class/input/event1
Accelerometer ---      /dev/input2  --- /sys/class/input/input2 --- /sys/class/input/event2
Touchscreen ---         /dev/input3  --- /sys/class/input/input3 --- /sys/class/input/event3 
... 6 more like this
(All these are created during boot up time)

Kernel has created all these nodes, so that HAL/UpperLayer can read or write values from it.
HAL/Upper-Layer needs to do main tasks like:
1. Read raw data - does through /dev/input<num>
2. Enable device - does through sys/class/input<num>/enable
3. Set delay - does through sys/class/input<num>/delay
and many more...

Now, Lets suppose we need to do these tasks for Accelerometer.

If dev node name is set, HAL can directly read value from it (no search required)
But for enabling the accelerometer device or set the delay of a hardware chip, 
there is no direct way, HAL can know which input node to refer for accelerometer
because the input number is created dynamically as per device probe order,
so this input number can be anything (0,1,2,3...)
So HAL will need to search every input node and read its name attribute
and keep on searching until a match is found between the "attribute name" and "name passed as parameter". 
Like for accelerometer, this searching needs to be done for all other input devices.
All of this part is done during booting and this takes a lot for time from booting perspective.

As I measured, if there are ten devices, it is taking 1 second to do all this searching. (for all devices)
So for 20 devices, i guess, it could take upto 2 seconds.

With naming convention, there is no need of search neither for dev path nor for sysfs path
because HAL directly know which node to refer for which input device
and hence this 1 second is reduced to 10ms or even less, therefore saving 990ms.
I believe, this is a very good time saving. (from device booting perspective)

(Is there any direct way, without scanning all nodes for every input device ?)

> 
> 2. Improves Readabilty of input and event sysfs node paths because
> names are used instead of numbers.

I do not see why it is that important. If one wants overview
/proc/bus/input/devices gives nice picture.

Re: (Aniroop Mathur)
Its correct, we can get an overview from /proc/bus/input/devices.
And therefore using this, we can know input node number for every input device.
But there are many input devices and input numbers are not fixed, 
so its quite difficult to memorize input number for all input devices.
Therefore, if a user needs to open some input node from sysfs path,
he needs to check /proc/bus/input/devices before opening because 
he does not know the input number. Moreover, this applies for all other
input devices and hence a user need to check this every time.

It improves readabilty as below

Before:				After patch:
/dev/input0				/dev/input_proximity
/dev/input1				/dev/input_accelerometer
...many more

/sys/class/input/input0			/sys/class/input/input_proximity
/sys/class/input/input1			/sys/class/input/input_accelerometer
...many more	

/sys/class/input/event0			/sys/class/input/event_proximity
/sys/class/input/event1			/sys/class/input/event_accelerometer
...many more

So, just by looking, user can directly open or refer any input node.
(no need to refer any other path)

> 
> 3. Removes Input Devices Dependency. If one input device probe fails,
> other input devices still work.  Before this patch, if one input
> device probe fails before input_register_device, then input number of
> other input devices changes and due to this permission settings are
> disturbed and hence HAL or upper layer cannot open the required sysfs
> node because permission denied error comes.

I have only one suggestion here: fix your userspace so that does not
depend on device initialization ordering.

Re: (Aniroop Mathur)
We cannot fix userspace because these input/event/dev number are decided/allocated in kernel
as per device initialization ordering during boot up. (userspace has no role in it)
So, userspace is not aware, which exact input number corresponds to which input device 
so it ends up searching/scanning every input node untill a match is found.

So, there is input device dependency which needs to be removed.

----------------------------

IOW I am totally unconvinced that this facility is needed.

Re: (Aniroop Mathur)
I hope my problem and suggestion is more clear and convincing now.


For reference, copying Patch again:

---
drivers/input/evdev.c |   11 ++++++++++-
drivers/input/input.c |   12 +++++++++++-
include/linux/input.h |    4 ++++
3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index b6ded17..b6a5848 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -1131,7 +1131,16 @@ static int evdev_connect(struct input_handler *handler, struct input_dev *dev,
/* Normalize device number if it falls into legacy range */
if (dev_no < EVDEV_MINOR_BASE + EVDEV_MINORS)
dev_no -= EVDEV_MINOR_BASE;
- dev_set_name(&evdev->dev, "event%d", dev_no);
+
+ /*
+ * As per user choice (driver),
+ * name of sysfs node is set, as mentioned in node_name_unique variable.
+ * If node_name_unique is not set, default name is given.
+ */
+ if (dev->node_name_unique)
+ dev_set_name(&evdev->dev, "event_%s", dev->node_name_unique);
+ else
+ dev_set_name(&evdev->dev, "event%d", dev_no);

evdev->handle.dev = input_get_device(dev);
evdev->handle.name = dev_name(&evdev->dev);
diff --git a/drivers/input/input.c b/drivers/input/input.c
index c044699..c8126b3 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -2073,7 +2073,17 @@ int input_register_device(struct input_dev *dev)
if (!dev->setkeycode)
dev->setkeycode = input_default_setkeycode;

- dev_set_name(&dev->dev, "input%ld",
+ /*
+ * As per user choice (driver),
+ * name of sysfs node is set, as mentioned in node_name_unique variable.
+ * If node_name_unique is not set, default name is given.
+ */
+ if (dev->node_name_unique) {
+ atomic_inc_return(&input_no);
+ dev_set_name(&dev->dev, "input_%s",
+      dev->node_name_unique);
+ } else
+ dev_set_name(&dev->dev, "input%ld",
     (unsigned long) atomic_inc_return(&input_no) - 1);

error = device_add(&dev->dev);
diff --git a/include/linux/input.h b/include/linux/input.h
index 82ce323..fe44643 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -43,6 +43,9 @@ struct input_value {
  * @uniq: unique identification code for the device (if device has it)
  * @id: id of the device (struct input_id)
  * @propbit: bitmap of device properties and quirks
+ * @node_name_unique: name of input and event sysfs device node (char *).
+ * This name must be unique among all input devices and driver(user)
+ * has the responsibility to ensure it (if using).
  * @evbit: bitmap of types of events supported by the device (EV_KEY,
  * EV_REL, etc.)
  * @keybit: bitmap of keys/buttons this device has
@@ -123,6 +126,7 @@ struct input_dev {
const char *phys;
const char *uniq;
struct input_id id;
+ char *node_name_unique;

unsigned long propbit[BITS_TO_LONGS(INPUT_PROP_CNT)];


Thanks,
Aniroop Mathur