linux-kernel - Re: [PATCH RFC 0/3] Implement refcounting for OF GPIO chips

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Date:	Tue, 9 Feb 2010 10:29:07 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	michal.simek@...alogix.com
Cc:	avorontsov@...mvista.com,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Michal Simek <monstr@...str.eu>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	microblaze-uclinux@...e.uq.edu.au
Subject: Re: [PATCH RFC 0/3] Implement refcounting for OF GPIO chips

On Tue, Feb 9, 2010 at 2:40 AM, Michal Simek <michal.simek@...alogix.com> wrote:
> Anton Vorontsov wrote:
>>
>> Hi all,
>>
>> OF GPIO infrastructure is using dynamic GPIO bases, so it is possible
>> that of_get_gpio()'s returned GPIO number will be no longer valid, or
>> worse, it may point to an unexpected GPIO controller.
>>
>> This scenario is possible:
>>
>> driver A:               driver B:              driver C:
>> ---------               ---------              ---------
>>                        gpiochip_add()
>> gpio = of_get_gpio()
>>                        gpiochip_remove()
>>                                               gpiochip_add()
>> gpio_request(gpio);
>> gpio_set_value(gpio);
>>
>> That is, driver A assumes that it is working with GPIO from driver B,
>> but in practice it may disappear and driver C will take its GPIO base
>> number, so it will provide the same GPIO numbers.
>>
>> The above situation is hard to trigger, but the issue is there
>> nonetheless, and so needs fixing.
>
>
> I tested xilinx gpio driver, heartbeat trigger and access through sysfs and
> I haven't found any problem. There is only small part of code for Microblaze
> and it is the same with PowerPC. If is Ben OK with it, I am ok too.

I'm not convinced the changes take the best approach, so I'm not okay
with it yet.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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