On Wed, Oct 20, 2021 at 4:14 AM Dmitry Torokhov
[off-list ref] wrote:

On Wed, Oct 20, 2021 at 11:44:50AM +1000, Alistair Francis wrote:

quoted

On Wed, Oct 20, 2021 at 11:05 AM Dmitry Torokhov
[off-list ref] wrote:

quoted

On Wed, Oct 20, 2021 at 09:33:13AM +1000, Alistair Francis wrote:

quoted

On Tue, Oct 19, 2021 at 11:51 AM Dmitry Torokhov
[off-list ref] wrote:

quoted

We already have touchscreen-inverted-x/y defined in
Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml,
why are they not sufficient?

The touchscreen-* properties aren't applied to HID devices though, at
least not that I can tell.

No, they are not currently, but that does not mean we need to establish
a new set of properties (property names) for HID case.

I can update the names to use the existing touchscreen ones.

Do you have a hint of where this should be implemented though?

Right now (without "HID: wacom: Add support for the AG14 Wacom
device") the wacom touchscreen is just registered as a generic HID
device. I don't see any good place in hid-core, hid-input or
hid-generic to invert the input values for this.

I think the transformation should happen in
hid-multitouch.c::mt_process_slot() using helpers from
include/linux/input/touchscreen.h

I think the more challenging question is to how pass/attach struct
touchscreen_properties * to the hid device (i expect the properties will
be attached to i2c-hid device, but maybe we could create a sub-node of
it and attach properties there.

Sorry but I don't like that very much. This would mean that we have an
out of band information that needs to be carried over to
HID-generic/multitouch and having tests for it is going to be harder.
I would rather have userspace deal with the rotation if we do not have
the information from the device itself.

Foreword: I have been given a hammer, so I see nails everywhere.

The past 3 weeks I have been working on implementing some eBPF hooks
in the HID subsystem. This would IMO be the best solution here: a udev
hwdb rule sees that there is the not-wacom PID/VID (and maybe the
platform or parses the OF properties if they are available in the
sysfs) and adds a couple of functions in the HID stack to rotate the
screen. The advantage is that we do not need to add a new kernel API
anymore, the disadvantage is that we need userspace to "fix" the
kernel behaviour (so at boot, this might be an issue).

I am not at the point where I can share the code as there is a lot of
rewriting and my last attempt is resulting in a page fault, but I'd be
happy to share it more once that hiccup is solved.

Cheers,
Benjamin


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