Dmitry,

Thanks you. I appreciate that your answered my questions.
I think now I agree we just stay with the current wacom_i2c.

This is just to tell you what kind of situation we deal with wacom_i2c with our customers.
We work with OEMs,/ODMs and they often want to add/customize their own features onto Wacom pen functionality with their Linux based OS, such as Chrome OS, Android, Linux desktop distribution, etc.
In those cases, some of them want to use wacom_i2c.
The reason is if they used wacom_i2c, they would be able to concentrate on their own desired programs.
Since wacom_i2c has simple structure for initialization - their desired special preparation- and for handling input events to add their specific purpose,
it is easier for OEMs/ODMs to handle such. On the other hand, they may have to look into whole hid codes throughout parsing hid collections when they
want to the same as I just described prior to this sentence; and it takes time more than they do with wacom_i2c. Also, finding problems becomes more difficult for them if they have.

We usually recommend the customers use i2c-hid, but not all of them follow it and use wacom_i2c with that reasons above.
We, this time, tried to update it because some of the customers try to use the current wacom_i2c as it is - compatible older generations of the products- and ask us the correct one.
Yes we do then, but we thought maybe updating wacom_i2c may help them use it easier.

That's it. I just want to tell you why we started suddenly update the driver.
Thanks,

Tats

-----Original Message-----
From: Dmitry Torokhov <dmitry.torokhov@gmail.com> 
Sent: Thursday, October 7, 2021 3:03 AM
To: Tobita, Tatsunosuke <redacted>
Cc: Ping Cheng <redacted>; Alistair Francis <redacted>; Cheng, Ping <Ping.Cheng@wacom.com>; linux-input <redacted>; linux-imx@nxp.com; kernel@pengutronix.de; Tatsunosuke Tobita <redacted>; linux-kernel@vger.kernel.org; alistair23@gmail.com; robh+dt@kernel.org; devicetree@vger.kernel.org
Subject: Re: [PATCH v10 05/12] Input: wacom_i2c - Read the descriptor values

[EXTERNAL]

Hi Tatsunosuke,

On Wed, Oct 06, 2021 at 07:08:38AM +0000, Tobita, Tatsunosuke wrote:

Hi Dmitry,

I now understand what you mean. The understandable example is USB. The 
most of the recent drivers for USB devices has bee released as HiD 
driver.  That said. It's glad if you can have comments too about my 
questions.  Especially, when someone doesn't want the whole HID 
driver, but a single I2C I/F'd input device driver.

So far I have not heard a good reason for "not wanting" to use a standard, well tested solution that everyone else is using, and instead having a custom driver that essentially reimplements everything that HID layer already does. Is the additional memory requirements of HID layer too onerous? Can we address that instead?

If we continue this train of thought, why are they concerned with HID, but happy with using I2C layer? Why don't they require a driver that bangs directly onto I2C master ports bypassing all the layersi and communicating with the peripheral directly?

And also, I want to make correction that ***not*** all of our devices 
support HID. Some old devices do not support HID; that's why I added 
the driver in 2011.

And that is a good reason to keep existing version of wacom_i2c in the kernel, but we should not try to extend it to handle HID-compatible devices.

Thanks,
Dmitry

Thanks,

Tats

-----Original Message-----
From: Tobita, Tatsunosuke <redacted>
Sent: Friday, September 10, 2021 1:10 PM
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>; Ping Cheng 
[off-list ref]
Cc: Alistair Francis <redacted>; Cheng, Ping 
[off-list ref]; linux-input [off-list ref]; 
linux-imx@nxp.com; kernel@pengutronix.de; Tatsunosuke Tobita 
[off-list ref]; linux-kernel@vger.kernel.org; 
alistair23@gmail.com; robh+dt@kernel.org; devicetree@vger.kernel.org
Subject: RE: [PATCH v10 05/12] Input: wacom_i2c - Read the descriptor 
values

[EXTERNAL]

Hi Dmitry and Ping,

I understand that we should stick with HID as much as possible.
However, there're certainly situations in which some do not want even whole HID, but only an individual functionality for a certain device.
In that case, they may not even include the bit of the HID, but exclude HID. What about then; what they should do without HID?
This would be also the questions if such situations happened to other vendors than Wacom.

Also, what I need to add is that the early generations of our I2C devices do not support HID which is why "wacom_i2c" was added in 2011.


Tats

-----Original Message-----
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Sent: Wednesday, September 8, 2021 2:56 PM
To: Ping Cheng <redacted>
Cc: Tobita, Tatsunosuke <redacted>; Alistair 
Francis [off-list ref]; Cheng, Ping [off-list ref]; 
linux-input [off-list ref]; linux-imx@nxp.com; 
kernel@pengutronix.de; Tatsunosuke Tobita [off-list ref]; 
linux-kernel@vger.kernel.org; alistair23@gmail.com; 
robh+dt@kernel.org; devicetree@vger.kernel.org
Subject: Re: [PATCH v10 05/12] Input: wacom_i2c - Read the descriptor 
values

[EXTERNAL]

Hi Ping,

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

quoted

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.

quoted

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