ABS_PRESSURE and 0 ranges

Hi all,

as I found out the hard way tslib does the detection if a touchscreen has been "clicked" if the kernel driver says it does not support ABS_PRESSURE. But when the kernel says it can do ABS_PRESSURE tslib will not do it's emulation and just pass on whatever pressure value the kernel sends.

So far, so good. Sadly there are some drivers that do:

input_set_abs_params(dev, ABS_PRESSURE, 0, 0, 0, 0);

Guess what happens: no clicks at all. The question I have is: does the above line make any sense to be in a kernel driver at all? Or is that some voodoo that must be there and it's all tslib fault?

Now that I know where the problem is coming from the problem is easily fixable, I'm just wondering which patch to make.

Hi Rolf,

Quoted 8 lines · Rolf Eike Beer

Hi all,

as I found out the hard way tslib does the detection if a touchscreen has been "clicked" if the kernel driver says it does not support ABS_PRESSURE. But when the kernel says it can do ABS_PRESSURE tslib will not do it's emulation and just pass on whatever pressure value the kernel sends.

Quoted 3 lines

So far, so good. Sadly there are some drivers that do:

input_set_abs_params(dev, ABS_PRESSURE, 0, 0, 0, 0);

What drivers are doing this?

Quoted 6 lines

Guess what happens: no clicks at all. The question I have is: does the above line make any sense to be in a kernel driver at all? Or is that some voodoo that must be there and it's all tslib fault?

Now that I know where the problem is coming from the problem is easily fixable, I'm just wondering which patch to make.

Well, the limits are strictly advisory for userspace, input core does not perform any clamping or discarding the data that falls outside the limits, so tslib probably should not do that either.

Quoted 13 lines · You

Hi Rolf,

Quoted 10 lines · Rolf Eike Beer

Hi all,

as I found out the hard way tslib does the detection if a touchscreen has
been "clicked" if the kernel driver says it does not support ABS_PRESSURE. But when the kernel says it can do ABS_PRESSURE tslib will not do it's emulation and just pass on whatever pressure value the kernel
sends.

Quoted 5 lines

Quoted 3 lines

So far, so good. Sadly there are some drivers that do:

input_set_abs_params(dev, ABS_PRESSURE, 0, 0, 0, 0);

What drivers are doing this?

git grep 'ABS_PRESSURE, 0, 0, 0, 0' drivers/input/

Quoted 10 lines

Quoted 6 lines

Guess what happens: no clicks at all. The question I have is: does the above line make any sense to be in a kernel driver at all? Or is that some voodoo that must be there and it's all tslib fault?

Now that I know where the problem is coming from the problem is easily fixable, I'm just wondering which patch to make.

Well, the limits are strictly advisory for userspace, input core does not perform any clamping or discarding the data that falls outside the limits, so tslib probably should not do that either.

My main concern is that if the driver says it will only ever give pressure values from 0 to 0, what useful stuff may that ever be? And since the driver says it supports presure touchscreen will wait for the driver to report it. Since it will never do it (or could at most return a 0), then there is nothing that could ever become a valid click event.

Quoted 34 lines · Rolf Eike Beer

Quoted 14 lines · You

Hi Rolf,

Quoted 11 lines · Rolf Eike Beer

Hi all,

as I found out the hard way tslib does the detection if a touchscreen has
been "clicked" if the kernel driver says it does not support ABS_PRESSURE. But when the kernel says it can do ABS_PRESSURE tslib will
not do it's emulation and just pass on whatever pressure value the kernel
sends.

Quoted 5 lines

Quoted 3 lines

So far, so good. Sadly there are some drivers that do:

input_set_abs_params(dev, ABS_PRESSURE, 0, 0, 0, 0);

What drivers are doing this?

git grep 'ABS_PRESSURE, 0, 0, 0, 0' drivers/input/

Quoted 10 lines

Quoted 6 lines

Guess what happens: no clicks at all. The question I have is: does the above line make any sense to be in a kernel driver at all? Or is that some voodoo that must be there and it's all tslib fault?

Now that I know where the problem is coming from the problem is easily fixable, I'm just wondering which patch to make.

Well, the limits are strictly advisory for userspace, input core does not perform any clamping or discarding the data that falls outside the limits, so tslib probably should not do that either.

Quoted 5 lines

My main concern is that if the driver says it will only ever give pressure values from 0 to 0, what useful stuff may that ever be? And since the driver says it supports presure touchscreen will wait for the driver to report it. Since it will never do it (or could at most return a 0), then there is nothing that could ever become a valid click event.

Once again, the limits are simply advisory and can even be adjusted from userspace (EVIOCSABS).

So ucb1400_ts does report true pressure so all is good there, but tsc40 is not. I think the claim for ABS_PRESSURE is left over from time when tslib did not think that device without ABS_PRESSURE was a touchscreen. I'll remove it from the driver.