Re: [PATCH v10 05/12] Input: wacom_i2c - Read the descriptor values

From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Ping Cheng <pinglinux@gmail.com>
Cc: "Tobita, Tatsunosuke" <tatsunosuke.tobita@wacom.com>,
	Alistair Francis <alistair@alistair23.me>,
	"Cheng, Ping" <Ping.Cheng@wacom.com>,
	linux-input <linux-input@vger.kernel.org>,
	linux-imx@nxp.com, kernel@pengutronix.de,
	Tatsunosuke Tobita <junkpainting@gmail.com>,
	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
Date: Tue, 7 Sep 2021 22:55:30 -0700	[thread overview]
Message-ID: <YThQUtE757b/ExR4@google.com> (raw)
In-Reply-To: <CAF8JNh+PcYuaLL=ToS0hOT62YbVmMWY9BCT-CGx_x+AkKuO_Tw@mail.gmail.com>

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 <dmitry.torokhov@gmail.com>
> wrote:
> 
> > Hi Tatsunosuke,
> >
> > On Thu, Sep 02, 2021 at 07:33:49AM +0000, Tobita, Tatsunosuke wrote:
> > > 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.
> 
> >
> There needs to be a _very_ strong reason to essentially duplicate
> > 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