Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230418124953.3170028-1-fshao@chromium.org> <20230418124953.3170028-2-fshao@chromium.org>
 <ZD8z57MBvcfExJx8@nixie71> <CAC=S1ngBt9DmBobMkQXWhqE1UUxFv2U6iFd42nT=1N7r8+pFUg@mail.gmail.com>
 <CAD=FV=U_i26a8uJYmqYf6PUgmTUgmEB5L2DkVga0zDX_iDcGQg@mail.gmail.com>
 <ZEAGTiGyvynGA9P1@nixie71> <CAD=FV=UB393Z1zhK54Apgr-iRcvgiK0t36jt6-t5-5zz3m8OZQ@mail.gmail.com>
 <CAC=S1nj8VTXOovvianPWDYnsrbek0APD76SBNquFObaw8Vg4BQ@mail.gmail.com>
 <ZEX4BEVMf6GtvaAP@nixie71> <CAD=FV=VtrJDVB0gQp-O82V3mgU6MFVMSGrvzh0fRa7sYAt_Pqw@mail.gmail.com>
In-Reply-To: <CAD=FV=VtrJDVB0gQp-O82V3mgU6MFVMSGrvzh0fRa7sYAt_Pqw@mail.gmail.com>
From:   Fei Shao <fshao@chromium.org>
Date:   Tue, 25 Apr 2023 16:34:16 +0800
Message-ID: <CAC=S1nhFNq_kK5zJCWQiGBuJbDXiC8BstJ5BT7pi5O8hLDQSfA@mail.gmail.com>
Subject: Re: [PATCH 1/2] dt-bindings: input: goodix: Add powered-in-suspend property
To:     Doug Anderson <dianders@chromium.org>
Cc:     Jeff LaBundy <jeff@labundy.com>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Rob Herring <robh+dt@kernel.org>,
        linux-mediatek <linux-mediatek@lists.infradead.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        devicetree@vger.kernel.org, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Apr 25, 2023 at 2:15=E2=80=AFAM Doug Anderson <dianders@chromium.or=
g> wrote:
>
> Hi,
>
> On Sun, Apr 23, 2023 at 8:31=E2=80=AFPM Jeff LaBundy <jeff@labundy.com> w=
rote:
> >
> > Back-powering can come in two forms:
> >
> > 1. The one you've described, which is by far the most common. As you me=
ntion,
> > it is not the case here since the issue happens only when we drive the =
GPIO
> > low and not high.
> >
> > 2. Through a forbidden power supply sequence, an input pin of an IC wit=
h
> > multiple power supplies becomes a weak power supply itself. Grounding t=
he
> > GPIO then sinks current into the SoC.
> >
> > This problem smelled like (2), especially since asserting the GPIO or p=
owering
> > down the supply alleviates the symptom. Most Goodix controllers I've wo=
rked
> > with have two or more supplies, and the datasheet requires them to be e=
nabled
> > or disabled in a specific order.
> >
> > Based on Fei's feedback, however, this IC does not seem to be one of th=
ose
> > since there is reportedly only a single rail. I guess either vdd or vdd=
io is
> > tied to a dummy regulator? If so, then perhaps we can scratch this theo=
ry.
>
> There is one rail provided from the main board, but there can be two
> voltage levels involved depending on stuffings on the touchscreen
> itself. I talked a bit about this in commit 1d18c1f3b7d9
> ("dt-bindings: HID: i2c-hid: goodix: Add mainboard-vddio-supply").
>
>
> > Fair enough, I was simply sketpical that this was the _right_ workaroun=
d.
> > Were this an issue of only supply A left on yet the IC datasheet requir=
es
> > supply B to remain on if supply A is on, I would rather see this solved=
 by
> > updating a regulator dts node, trusted FW sequence, etc.
>
> Right. That type of stuff was looked at in detail by two separate
> teams, so I don't think this is the issue.
>
>
> > Thanks for your due diligence; if this really is a silicon issue, then
> > the driver should indeed accommodate it.
> >
> > That being said, the name 'powered-in-suspend' seems a bit conflated. W=
e
> > should not be duplicating regulator policy in this driver; the existing
> > naming also may cause confusion for other HW configurations that do lea=
ve
> > vdd and vddio on during suspend, but don't have this problem.
> >
> > Here, we actually mean to control the behavior of the reset GPIO throug=
h
> > suspend and therefore something like 'goodix,no-reset-during-suspend' i=
s
> > closer to what I understand us to intend to do. I will add more details
> > in patch [2/2].
>
> I'd be fine with that name. ...ah, and adding the "goodix," prefix is
> a good call.
>
> -Doug

That sounds good to me, too. I'll update the name in the next patch.

Regards,
Fei