linux-kernel - Re: [PATCH v2] gpio: winbond: add driver

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Date:   Wed, 27 Dec 2017 12:16:53 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jonathan Cameron <jic23@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH v2] gpio: winbond: add driver

On Wed, Dec 27, 2017 at 1:24 AM, William Breathitt Gray
<vilhelm.gray@...il.com> wrote:

> Here are the error messages printed on my system when I add a select
> ISA_BUS_API line to the GPIO_WINBOND Kconfig option in the version 2 of
> your patch:
>
> drivers/gpio/Kconfig:13:error: recursive dependency detected!
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/gpio/Kconfig:13:        symbol GPIOLIB is selected by STX104
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/iio/adc/Kconfig:659:    symbol STX104 depends on ISA_BUS_API
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> arch/Kconfig:818:       symbol ISA_BUS_API is selected by GPIO_WINBOND
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/gpio/Kconfig:701:       symbol GPIO_WINBOND depends on GPIOLIB

So STX104 depends on ISA_BUS_API which in turn is
selected by GPIO_WINBOND which also depends on GPIOLIB.

> The issue seems to relate to the select GPIOLIB line for the STX104
> Kconfig option (which has a ISA_BUS_API dependency). Switching GPIOLIB
> to be a dependency, or alternatively selecting ISA_BUS_API, alleviates
> the recursion.
>
> Linus, is my use of select GPIOLIB for the STX104 Kconfig option
> appropriate in this context -- or should it instead be part of the
> depends on line? The STX104 driver includes linux/gpio/driver.h and
> makes use of the devm_gpiochip_add_data function to add support for some
> minor auxililary GPIO lines on the STX104 device.

In the STX104 case, it seems to be appropriate to
select GPIOLIB, as it is a GPIO provider, not consumer.

Usually I prefer that drivers just select what they need so I don't
have to run around in the whole kernel tree and turn things on
to the left and right before I can finally select my driver, but
maybe that is just me.

The other ISA GPIO drivers depends on ISA_BUS_API, I guess
in difference from the symbol GPIOLIB it cannot be universally
selected, so shouldn't this driver also just depends on ISA_BUS_API
and select it from the machine or wherever?

Yours,
Linus Walleij