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From:   Michael Walle <michael@walle.cc>
To:     marcelo.jimenez@gmail.com
Cc:     achant@google.com, brgl@bgdev.pl, edmondchung@google.com,
        geert@linux-m68k.org, linus.walleij@linaro.org,
        linux-gpio@vger.kernel.org, regressions@lists.linux.dev,
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        tanzilli@acmesystems.it, treding@nvidia.com, vidyas@nvidia.com,
        willmcvicker@google.com,
        Horatiu Vultur <horatiu.vultur@microchip.com>,
        Lars Povlsen <lars.povlsen@microchip.com>,
        Michael Walle <michael@walle.cc>
Subject: Re: [PATCH] gpio: Revert regression in sysfs-gpio (gpiolib.c)
Date:   Mon, 14 Mar 2022 16:55:09 +0100
Message-Id: <20220314155509.552218-1-michael@walle.cc>
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Hi,

> Some GPIO lines have stopped working after the patch
> commit 2ab73c6d8323f ("gpio: Support GPIO controllers without pin-ranges")
> 
> And this has supposedly been fixed in the following patches
> commit 89ad556b7f96a ("gpio: Avoid using pin ranges with !PINCTRL")
> commit 6dbbf84603961 ("gpiolib: Don't free if pin ranges are not defined")
> 
> But an erratic behavior where some GPIO lines work while others do not work
> has been introduced.
> 
> This patch reverts those changes so that the sysfs-gpio interface works
> properly again.
> 
> Signed-off-by: Marcelo Roberto Jimenez <marcelo.jimenez@gmail.com>

This breaks the pinctrl-microchip-sgpio driver as far as I can see.

I tried to debug it and this is what I have discovered so far:
 (1) the sgpio driver will use the gpio_stub_drv for its child nodes.
     Looks like a workaround, see [1].
 (2) these will have an empty gpio range
 (3) with the changes of this patch, pinctrl_gpio_request() will now
     be called and will fail with -EPROBE_DEFER.

I'm not exactly sure what to do here. Saravana Kannan once suggested
to use devm_of_platform_populate() to probe the child nodes [2]. But
I haven't found any other driver doing that.

Also, I'm not sure if there are any other other driver which get
broken by this. I.e. ones falling into the gpio_stub_drv category.

[1] https://lore.kernel.org/lkml/20210122193600.1415639-1-saravanak@google.com/
[2] https://lore.kernel.org/lkml/CAGETcx9PiX==mLxB9PO8Myyk6u2vhPVwTMsA5NkD-ywH5xhusw@mail.gmail.com/

-michael

NB. this patch doesn't contain a Fixes tag. Was this on purpose?