linux-kernel - Re: [PATCH v4 00/10] gpio: improve support for shared GPIOs

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Message-ID: <e27e1a6b-53ae-4416-8322-dbfb1c212755@kernel.org>
Date: Fri, 21 Nov 2025 11:20:20 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>, Val Packett <val@...kett.cool>
Cc: Kees Cook <kees@...nel.org>, Mika Westerberg <westeri@...nel.org>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Linus Walleij <linus.walleij@...aro.org>,
 Manivannan Sadhasivam <mani@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Andy Shevchenko <andy@...nel.org>, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Srinivas Kandagatla <srini@...nel.org>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, Alexey Klimov <alexey.klimov@...aro.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, linux-hardening@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-sound@...r.kernel.org,
 linux-arm-msm@...r.kernel.org,
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v4 00/10] gpio: improve support for shared GPIOs

On 21/11/2025 10:03, Bartosz Golaszewski wrote:
> On Fri, Nov 21, 2025 at 1:28 AM Val Packett <val@...kett.cool> wrote:
>>
>> Hi,
>>
>> On 11/12/25 10:55 AM, Bartosz Golaszewski wrote:
>>> ---
>>> Bartosz Golaszewski (10):
>>>        string: provide strends()
>>>        gpiolib: define GPIOD_FLAG_SHARED
>>>        gpiolib: implement low-level, shared GPIO support
>>>        gpio: shared-proxy: implement the shared GPIO proxy driver
>>>        gpiolib: support shared GPIOs in core subsystem code
>>>        gpio: provide gpiod_is_shared()
>>>        arm64: select HAVE_SHARED_GPIOS for ARCH_QCOM
>>>        ASoC: wsa881x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup
>>>        ASoC: wsa883x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup
>>>        regulator: make the subsystem aware of shared GPIOs
>>
>> this seems to actually have caused a regression for me, audio does not
>> initialize anymore on hamoa due to EBUSY since upgrading
>> from next-20251114 to next-20251118 or next-20251120:
>>
> 
> Thanks for the heads-up.
> 
>> [   11.748781] platform
>> 6800000.remoteproc:glink-edge:gpr:service@1:dais: Adding to iommu group 30
>> [   11.785864] wsa_macro 6aa0000.codec: using zero-initialized flat
>> cache, this may cause unexpected behavior
>> [   11.796964] reset-gpio reset-gpio.0: error -EBUSY: Could not get
>> reset gpios
>> [   11.796984] reset-gpio reset-gpio.0: probe with driver reset-gpio
>> failed with error -16
>> [   11.894662] reset-gpio reset-gpio.1: error -EBUSY: Could not get
>> reset gpios
>> [   11.894676] reset-gpio reset-gpio.1: probe with driver reset-gpio
>> failed with error -16
> 
> It seems like it's the reset-gpio driver, not shared GPIOLIB path?
> This driver has never used the GPIOD_FLAGS_BIT_NONEXCLUSIVE flag.

NONEXCLUSIVE does not matter here. I think this is just broken code -
your patch 3 goes through allnodes for_each_property_of_node() and then
assumes it is shared GPIO, so probably this nicely breaks existing DTS
and reset-gpio. Well, it is not a shared GPIO, so all your assumptions
here are just wrong.

reset-gpio is already used on multiple Qualcomm and other SoC  platforms.

Best regards,
Krzysztof