linux-kernel - Re: [PATCH] pinctrl: qcom: Fix behavior in abscense of open-drain support

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Date: Fri, 3 May 2024 09:28:41 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>, Brian Norris <computersforpeace@...il.com>, 
	Jaiganesh Narayanan <njaigane@...eaurora.org>, Johan Hovold <johan@...nel.org>, 
	Doug Anderson <dianders@...omium.org>, linux-arm-msm@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pinctrl: qcom: Fix behavior in abscense of open-drain support

On Thu, Apr 25, 2024 at 5:46 AM Bjorn Andersson
<quic_bjorande@...cinc.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@...cinc.com>

I tried to follow the discussion but couldn't get to a verdict on this patch,
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