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From:   Svyatoslav Ryhel <clamor95@gmail.com>
Date:   Sun, 30 Jul 2023 21:21:19 +0300
Message-ID: <CAPVz0n1WUm6tg4Uhp8US_-1A5gBoJXAenqBz-EhVBNTmyC2=dg@mail.gmail.com>
Subject: Re: [PATCH v3 0/2] GPIO-based hotplug i2c bus
To:     Andi Shyti <andi.shyti@kernel.org>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Wolfram Sang <wsa@kernel.org>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>,
        linux-i2c@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
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=D0=BD=D0=B4, 30 =D0=BB=D0=B8=D0=BF. 2023=E2=80=AF=D1=80. =D0=BE 20:49 Andi=
 Shyti <andi.shyti@kernel.org> =D0=BF=D0=B8=D1=88=D0=B5:
>
> Hi Svyatoslav,
>
> On Sat, Jul 29, 2023 at 07:08:55PM +0300, Svyatoslav Ryhel wrote:
> > ASUS Transformers require this driver for proper work with their dock.
> > Dock is controlled by EC and its presence is detected by a GPIO.
> >
> > The Transformers have a connector that's used for USB, charging or
> > for attaching a keyboard (called a dock; it also has a battery and
> > a touchpad). This connector probably (I don't have the means to verify
> > that) has an I2C bus lines and a "detect" line (pulled low on the dock
> > side) among the pins. I guess there is either no additional chip or
> > a transparent bridge/buffer chip, but nothing that could be controlled
> > by software. For DT this setup could be modelled like an I2C gate or
> > a 2-port mux with enable joining two I2C buses (one "closer" to the
> > CPU as a parent).
> >
> > In this case it's hard to tell the difference if this is real or virtua=
l
> > hardware.
>
> How did you test this device?
>
Using devices, which relay on this patch, here is a list of those:
- ASUS Eee Pad Transformer TF101 (mainlined)
- ASUS Transformer Prime TF201 (mainlined)
- ASUS Transformer Pad TF300T/TF300TG/TF300TL (mainlined)
- ASUS Transformer Infinity TF700T (mainlined)
- ASUS VivoTab RT TF600T (WIP)
- ASUS Transformer Pad TF701T (mainlined)

Non ASUS device is Microsoft Surface RT

Tested by many owners and users for more than a year iirc.

> > This patchset is a predecessor of a possible larger patchset which
> > should bring support for a asus-ec, an i2c mfd device programmed by
> > Asus for their Transformers tablet line. Similar approach is used in
> > Microsoft Surface RT for attachable Type Cover.
>
> Would be nice to have a driver using this support in the series,
> otherwise it looks like thrown there without any use. Do you have
> any use of it already? Even in your private repository just to
> take a look.
>

Bindings which call gpio hotplug i2c bus:
ASUS TF https://github.com/clamor-s/linux/commit/360f62f706670ab13101ef15b7=
f2bc8880da7a48
ASUS TF600T/TF701T
https://github.com/clamor-s/linux/blob/transformer/arch/arm/boot/dts/tegra3=
0-asus-tf600t.dts#L1050-L1089
Surface RT https://github.com/grate-driver/linux/blob/master/arch/arm/boot/=
dts/tegra30-microsoft-surface-rt.dts#L35-L53

> Thanks,
> Andi