Hello Mr. Torokhov,

First of all, Thank you for your reply.

On Sat, Apr 2, 2016 at 3:21 AM, Dmitry Torokhov
[off-list ref] wrote:

quoted

On Fri, Mar 11, 2016 at 12:26:57AM +0530, Aniroop Mathur wrote:

quoted

Hi Henrik,

On Thu, Mar 10, 2016 at 7:15 PM, Henrik Rydberg [off-list ref] wrote:

quoted

Hi Dmitry,

quoted

quoted

diff --git a/drivers/input/input.c b/drivers/input/input.c
index 8806059..262ef77 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c

@@ -401,8 +401,7 @@ static void input_handle_event(struct input_dev *dev,
                if (dev->num_vals >= 2)
                        input_pass_values(dev, dev->vals, dev->num_vals);
                dev->num_vals = 0;
-       } else if (dev->num_vals >= dev->max_vals - 2) {
-               dev->vals[dev->num_vals++] = input_value_sync;
+       } else if (dev->num_vals >= dev->max_vals - 1) {
                input_pass_values(dev, dev->vals, dev->num_vals);
                dev->num_vals = 0;
        }

This makes sense to me. Henrik?

I went through the commits that made these changes, and I cannot see any strong
reason to keep it. However, this code path only triggers if no SYN events are
seen, as in a driver that fails to emit them and consequently fills up the
buffer. In other words, this change would only affect a device that is already,
to some degree, broken.

So, the question to Aniroop is: do you see this problem in practise, and in that
case, for what driver?

Nope. So far I have not dealt with any such driver.
I made this change because it is breaking protocol of SYN_REPORT event code.

Further from the code, I could deduce that max_vals is just an estimation of
packet_size and it does not guarantee that packet_size is same as max_vals.
So real packet_size can be more than max_vals value and hence we could not
insert SYN_REPORT until packet ends really.
Further, if we consider that there exists a driver or will exist in future
which sets capability of x event code according to which max_value comes out to
y and the real packet size is z i.e. driver wants to send same event codes
again in the same packet, so input event reader would be expecting SYN_REPORT
after z events but due to current code SYN_REPORT will get inserted
automatically after y events, which is a wrong behaviour.

Well, I think I agree with Aniroop that even if driver is to a degree
broken we should not be inserting random SYN_REPORT events into the
stream. I wonder if we should not add WARN_ONCE() there to highlight
potential problems with the way we estimate the number of events.

However I think there is an issue with the patch. If we happen to pass
values just before the final SYN_REPORT sent by the driver then we reset
dev->num_vals to 0 and will essentially suppress the final SYN_REPORT
event, which is not good either.

Yes, right!

I think it can be fixed by sending the rest of events but not the last event
in case number of events becomes greater than max_vals. The last event will be
saved to be sent in next set of events. This way immediate SYN_REPORT will not
be suppressed and duplicate SYN_REPORT event will not be sent as well.

Change:

@@ -401,8 +401,7 @@ static void input_handle_event(struct input_dev *dev,
                if (dev->num_vals >= 2)
                        input_pass_values(dev, dev->vals, dev->num_vals);
                dev->num_vals = 0;
-       } else if (dev->num_vals >= dev->max_vals - 2) {
-               dev->vals[dev->num_vals++] = input_value_sync;
-               input_pass_values(dev, dev->vals, dev->num_vals);
-               dev->num_vals = 0;
+       } else if (dev->num_vals == dev->max_vals) {
+                input_pass_values(dev, dev->vals, dev->num_vals - 1);
+                dev->num_vals = 0;
+                dev->vals[dev->num_vals++] = dev->vals[dev->max_vals - 1];
        }

So, does the above patch looks good now?