netdev - Re: [PATCH 2/2] gpio: gpiolib: set gpiochip

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Date:	Fri, 30 May 2014 20:16:59 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	David Daney <ddaney.cavm@...il.com>
CC:	abdoulaye berthe <berthe.ab@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>, m@...s.ch,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	patches@...nsource.wolfsonmicro.com,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	linux-samsungsoc@...r.kernel.org, spear-devel@...t.st.com,
	platform-driver-x86@...r.kernel.org,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	driverdevel <devel@...verdev.osuosl.org>
Subject: Re: [PATCH 2/2] gpio: gpiolib: set gpiochip_remove retval to void

On 05/30/2014 07:33 PM, David Daney wrote:
> On 05/30/2014 04:39 AM, Geert Uytterhoeven wrote:
>> On Fri, May 30, 2014 at 1:30 PM, abdoulaye berthe <berthe.ab@...il.com>
>> wrote:
>>> --- a/drivers/gpio/gpiolib.c
>>> +++ b/drivers/gpio/gpiolib.c
>>> @@ -1263,10 +1263,9 @@ static void gpiochip_irqchip_remove(struct
>>> gpio_chip *gpiochip);
>>>    *
>>>    * A gpio_chip with any GPIOs still requested may not be removed.
>>>    */
>>> -int gpiochip_remove(struct gpio_chip *chip)
>>> +void gpiochip_remove(struct gpio_chip *chip)
>>>   {
>>>          unsigned long   flags;
>>> -       int             status = 0;
>>>          unsigned        id;
>>>
>>>          acpi_gpiochip_remove(chip);
>>> @@ -1278,24 +1277,15 @@ int gpiochip_remove(struct gpio_chip *chip)
>>>          of_gpiochip_remove(chip);
>>>
>>>          for (id = 0; id < chip->ngpio; id++) {
>>> -               if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags)) {
>>> -                       status = -EBUSY;
>>> -                       break;
>>> -               }
>>> -       }
>>> -       if (status == 0) {
>>> -               for (id = 0; id < chip->ngpio; id++)
>>> -                       chip->desc[id].chip = NULL;
>>> -
>>> -               list_del(&chip->list);
>>> +               if (test_bit(FLAG_REQUESTED, &chip->desc[id].flags))
>>> +                       panic("gpio: removing gpiochip with gpios still
>>> requested\n");
>>
>> panic?
>
> NACK to the patch for this reason.  The strongest thing you should do here
> is WARN.
>
> That said, I am not sure why we need this whole patch set in the first place.

Well, what currently happens when you remove a device that is a provider of 
a gpio_chip which is still in use, is that the kernel crashes. Probably with 
a rather cryptic error message. So this patch doesn't really change the 
behavior, but makes it more explicit what is actually wrong. And even if you 
replace the panic() by a WARN() it will again just crash slightly later.

This is a design flaw in the GPIO subsystem that needs to be fixed.

- Lars
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