On 07/05/2011 03:50 PM, Daniel Kurtz wrote:

On Wed, Jul 6, 2011 at 1:42 AM, Chase Douglas
[off-list ref] wrote:

quoted

On 06/28/2011 10:07 PM, djkurtz@chromium.org wrote:

quoted

From: Daniel Kurtz <redacted>

Synaptics touchpads report increasing y from bottom to top.
This is inverted from normal userspace "top of screen is 0" coordinates.
Thus, the kernel driver reports inverted y coordinates to userspace.

In some cases, however, y = 0 is sent by the touchpad.
In these cases, the kernel driver should not invert, and just report 0.

Under what cases is y sent as 0, and why do we want to report it as 0 to
userspace?

I know of two such cases for the image sensor:
  (1) When all fingers, save the first finger are removed, an AGM
packet with (x=0, y=0, z=0) is sent.
  (2) When all fingers are removed, an SGM packet with (x=0, y=0, z=0) is sent.

After uploading this patch set, I played with the profile sensor
again, and I also saw it sometimes sends y=1 packets.  I don't know
what those are.

This is mostly useful for debugging the kernel driver.
When observing the raw position values, the special 0 (and 1?) cases
are more obvious when not inverted.
I think I am misleading in my commit message.  I don't believe these
are actually ever passed through to userspace.

If they are set, then they are passed through evdev, unless I'm missing
something... Given the cases listed above, it seems like we should be
special casing these scenarios. Maybe that means dropping the event or
handling finger count transitions or something else.

I'm happy with the patch as a cleanup of y inversion, but I don't see
the utility of passing y = 0 through. With all the debugging techniques
we have (printk, systemtap, perf, ftrace, etc.), I don't think we need
this functionality, and it might lead a code reviewer to scratch their
head wondering what the point was :).

Thanks!

-- Chase