From: Rob Herring <robh@kernel.org>
To: Jiri Kosina <jikos@kernel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Doug Anderson <dianders@chromium.org>,
Brian Norris <briannorris@chromium.org>,
Caesar Wang <wxt@rock-chips.com>,
"open list:ARM/Rockchip SoC..."
<linux-rockchip@lists.infradead.org>,
"linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support
Date: Fri, 9 Dec 2016 09:01:18 -0600 [thread overview]
Message-ID: <CAL_JsqLpjhHeeKq3PmNToux1Rgkg0M84-dv9HGCOws223ima4w@mail.gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1612091532240.16984@cbobk.fhfr.pm>
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
next prev parent reply other threads:[~2016-12-09 15:01 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-01 1:21 [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support Brian Norris
2016-12-01 1:21 ` [PATCH v2 2/2] HID: i2c-hid: support Wacom digitizer + regulator Brian Norris
2016-12-01 14:41 ` Benjamin Tissoires
2016-12-01 17:30 ` Brian Norris
2016-12-01 14:34 ` [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support Benjamin Tissoires
2016-12-01 17:24 ` Brian Norris
2016-12-05 23:59 ` Rob Herring
2016-12-06 0:16 ` Dmitry Torokhov
2016-12-06 8:48 ` Benjamin Tissoires
2016-12-06 14:56 ` Rob Herring
2016-12-06 16:18 ` Doug Anderson
2016-12-08 15:41 ` Benjamin Tissoires
2016-12-08 16:03 ` Rob Herring
2016-12-08 16:13 ` Dmitry Torokhov
2016-12-08 16:26 ` Rob Herring
2016-12-08 18:12 ` Dmitry Torokhov
2016-12-09 14:36 ` Rob Herring
2016-12-09 14:36 ` Jiri Kosina
2016-12-09 15:01 ` Rob Herring [this message]
2016-12-09 16:16 ` Doug Anderson
2016-12-12 8:53 ` Jiri Kosina
2016-12-12 10:01 ` Benjamin Tissoires
2016-12-12 14:47 ` Rob Herring
2016-12-12 18:34 ` Brian Norris
2016-12-13 22:10 ` Rob Herring
2016-12-08 16:01 ` Rob Herring
2016-12-09 16:05 ` Doug Anderson
2016-12-09 17:44 ` Rob Herring
2016-12-05 23:42 ` Rob Herring
2016-12-05 23:54 ` Brian Norris
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