Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support

From	Rob Herring <robh@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support
Date	2016-12-09 16:10 +0100
Message-ID	<sMuY9-4Pn-5@gated-at.bofh.it> (permalink)
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On Fri, Dec 9, 2016 at 8:36 AM, Jiri Kosina <jikos@kernel.org> wrote:
> On Thu, 8 Dec 2016, Rob Herring wrote:
>
>> > And if tomorrow there is Elan device that is drop-in compatible (same
>> > connector, etc) with Wacom i2c-hid, will you ask for Elan-specific
>> > binding? Atmel? Weida? They all need to be powered up ultimately.
>>
>> Yes, I will.
>
> What advantage does that bring?
>
>> That in no way means the OS driver has to know about each and every one.
>> If they can all claim compatibility with Wacom (including power
>> control), then they can have a Wacom compatible string too. Or you can
>> just never tell me that there's a different manufacturer and I won't
>> care as long you don't need different control. But soon as a device
>> needs another power rail, GPIO or different timing, then you'd better
>> have a new compatible string.
>
> Again, I simply don't understand what advantage does the aproach you are
> trying to use bring.

This is simply how DT works. HID-over-I2C devices are no different
than any other I2C device or any other component. You are not special.

> HID over I2C is a generic protocol.

DT describes h/w, not protocols.

> Sure, we need to have quirks for
> device-specific bugs, and in such cases enumerate particular devices. But
> we don't need DT for that at all.

When it is related to powering on the device you may need to know the
specific device in DT. Compatibles are like VID/PID for devices, a
unique identifier for the specific device. Having that does not to
prevent generic/common drivers. The same rules apply. You wouldn't
want different devices having the same VID/PID (surely that has never
happened) or only change a VID/PID when you find a bug. The same rules
apply for compatible strings. You should be able to apply quirks
without changing/adding compatible strings (or more generally, without
changing the dtb). Just like you wouldn't change a VID/PID for a
device only when you find a bug, you can't add/change a DT compatible.

BTW, As you do have a VID/PID, you could define a compatible string
syntax using VID/PID like is done for PCI and USB.

Rob

Thread

[PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support Brian Norris <briannorris@chromium.org> - 2016-12-01 02:30 +0100
  [PATCH v2 2/2] HID: i2c-hid: support Wacom digitizer + regulator Brian Norris <briannorris@chromium.org> - 2016-12-01 02:30 +0100
    Re: [PATCH v2 2/2] HID: i2c-hid: support Wacom digitizer + regulator Benjamin Tissoires <benjamin.tissoires@redhat.com> - 2016-12-01 15:50 +0100
      Re: [PATCH v2 2/2] HID: i2c-hid: support Wacom digitizer + regulator Brian Norris <briannorris@chromium.org> - 2016-12-01 18:40 +0100
  Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Benjamin Tissoires <benjamin.tissoires@redhat.com> - 2016-12-01 15:40 +0100
    Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Brian Norris <briannorris@chromium.org> - 2016-12-01 18:30 +0100
      Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-06 01:00 +0100
        Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-12-06 01:40 +0100
        Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Benjamin Tissoires <benjamin.tissoires@redhat.com> - 2016-12-06 09:50 +0100
          Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-06 16:00 +0100
            Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Doug Anderson <dianders@chromium.org> - 2016-12-06 17:20 +0100
              Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Benjamin Tissoires <benjamin.tissoires@redhat.com> - 2016-12-08 16:50 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-08 17:10 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-12-08 17:20 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-08 17:30 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-12-08 19:20 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-09 15:40 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Jiri Kosina <jikos@kernel.org> - 2016-12-09 15:40 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-09 16:10 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Doug Anderson <dianders@chromium.org> - 2016-12-09 17:20 +0100
              Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-08 17:10 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Doug Anderson <dianders@chromium.org> - 2016-12-09 17:10 +0100
                Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-09 18:50 +0100
  Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Rob Herring <robh@kernel.org> - 2016-12-06 00:50 +0100
    Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer +  regulator support Brian Norris <briannorris@chromium.org> - 2016-12-06 01:00 +0100

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