Received-SPF: pass (google.com: domain of linux-kernel+bounces-167318-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240424-tlmm-open-drain-v1-1-9dd2041f0532@quicinc.com>
In-Reply-To: <20240424-tlmm-open-drain-v1-1-9dd2041f0532@quicinc.com>
From: Linus Walleij <linus.walleij@linaro.org>
Date: Fri, 3 May 2024 09:28:41 +0200
Message-ID: <CACRpkdYw8jzFH5n377G76iMqri70Tf-1Vc=P5D6ESU_U0qRXWQ@mail.gmail.com>
Subject: Re: [PATCH] pinctrl: qcom: Fix behavior in abscense of open-drain support
To: Bjorn Andersson <quic_bjorande@quicinc.com>
Cc: Bjorn Andersson <andersson@kernel.org>, Brian Norris <computersforpeace@gmail.com>, 
	Jaiganesh Narayanan <njaigane@codeaurora.org>, Johan Hovold <johan@kernel.org>, 
	Doug Anderson <dianders@chromium.org>, linux-arm-msm@vger.kernel.org, 
	linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, Apr 25, 2024 at 5:46=E2=80=AFAM Bjorn Andersson
<quic_bjorande@quicinc.com> wrote:

> When a GPIO is configured as OPEN_DRAIN gpiolib will in
> gpiod_direction_output() attempt to configure the open-drain property of
> the hardware and if this fails fall back to software emulation of this
> state.
>
> The TLMM block in most Qualcomm platform does not implement such
> functionality, so this call would be expected to fail. But due to lack
> of checks for this condition, the zero-initialized od_bit will cause
> this request to silently corrupt the lowest bit in the config register
> (which typically is part of the bias configuration) and happily continue
> on.
>
> Fix this by checking if the od_bit value is unspecified and if so fail
> the request to avoid the unexpected state, and to make sure the software
> fallback actually kicks in.
>
> It is assumed for now that no implementation will come into existence
> with BIT(0) being the open-drain bit, simply for convenience sake.
>
> Fixes: 13355ca35cd1 ("pinctrl: qcom: ipq4019: add open drain support")
> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>

I tried to follow the discussion but couldn't get to a verdict on this patc=
h,
should it be applied or not, and if it should be applied, should the Fixes:
tag be dropped or left and considered a nonurgent fix as it does not
affect current behaviour?

Yours,
Linus Walleij