Hi Ping,

On Tue, Sep 07, 2021 at 10:25:43PM -0700, Ping Cheng wrote:

Hi Dmitry,

On Mon, Sep 6, 2021, 11:05 PM Dmitry Torokhov [off-list ref]
wrote:

quoted

Hi Tatsunosuke,

On Thu, Sep 02, 2021 at 07:33:49AM +0000, Tobita, Tatsunosuke wrote:

quoted

Hi Dmitry,

Yes, our firmware supports HID over I2C.  However, some of our
customers often do not want to use HID to handle our hardware; even
they don't install the generic HID driver neither.  In such case, we
need to distinguish what generation of our device customer's has. And
to do so, we check I2C HID descriptor even though the driver is not
working with HID driver components, but this one.  That is why I2C HID
descriptor is used there. It is called, but the situation with this
driver is not supposed to work as a HID device.

I would like to understand better why the customers do not want to use
HID.

Those customers normally run embedded Linux. Their hardwares have very
specific use cases. They don't need to support any other HID devices except
the Wacom i2c device.

quoted

There needs to be a _very_ strong reason to essentially duplicate

quoted

HID layer in a vendor driver and I inclined to say that such customers

would need to patch their kernels themselves.


They most likely don't want to duplicate HID layer. They just don't need
most of the HID layer code.

They just need touchscreen support. Plus stylus support. And maybe
battery support. And maybe something else down the road... And they need
to introduce DT and ACPI descriptors to be able to mould the behavior to
platform needs. Which is pretty much the purpose of HID layer.

wacom_i2c simplifies their deployment and
testing process. Most of those customers are very small companies...

And now please continue this train of thoughts and consider every touch
vendor. Wacom is not unique. We have Elan, Cypress, Weida, Goodix, etc.
etc. Vendor drivers were acceptable before we had I2C standard, but now
it is much better for everyone to share the efforts and use HID instead
of replicating it for every vendor.

Thanks.

-- 
Dmitry