Re: [PATCH 02/12] Input: synaptics - do not invert y if 0

Daniel Kurtz
2011-07-05T23:15:35Z

On Wed, Jul 6, 2011 at 7:06 AM, Chase Douglas
<chase.douglas@canonical.com> wrote:
> On 07/05/2011 03:50 PM, Daniel Kurtz wrote:
>> On Wed, Jul 6, 2011 at 1:42 AM, Chase Douglas
>> <chase.douglas@canonical.com> wrote:
>>>
>>> On 06/28/2011 10:07 PM, djkurtz@chromium.org wrote:
>>>> From: Daniel Kurtz <djkurtz@chromium.org>
>>>>
>>>> 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 :).

I meant if you were to printk y, it is much more obvious to see y=0
than y=5321 or something like that.
I don't think this reaches userspace because y=0 packets are usually
filtered out since z and x are also 0.

I guess this is the point, actually, that wasn't clear to me in
Henrik's astute observation:
We should do the conversion when reporting to userspace. Thus, only
do the conversion for packets that aren't already masked!

I will refactor to an inline function, but put the conversion back in
the input_report_abs() calls.

-Dan

>
> Thanks!
>
> -- Chase
>