Re: ABS_PRESSURE and 0 ranges

[Rolf Eike Beer <eike-kernel@sf-tec.de>]

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You wrote:
> On Thursday, October 25, 2012 10:11:27 PM Rolf Eike Beer wrote:
> > You wrote:
> > > Hi Rolf,
> > > 
> > > On Thu, Oct 25, 2012 at 02:59:49PM +0200, Rolf Eike Beer wrote:
> > > > 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);
> > > 
> > > What drivers are doing this?
> > 
> > git grep 'ABS_PRESSURE, 0, 0, 0, 0' drivers/input/
> > 
> > > > 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.
> 
> 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.

Thanks, so I know what part to patch. Please backport that to stable, too, so 
tslib will work with that driver even on stable kernels.

Eike

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