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

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Date:	Tue, 09 Feb 2010 10:40:53 +0100
From:	Michal Simek <michal.simek@...alogix.com>
To:	avorontsov@...mvista.com
CC:	Grant Likely <grant.likely@...retlab.ca>,
	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

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 that of_get_gpio()'s returned GPIO number will be no longer valid, or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.

Thanks,
Michal


> 
> Thanks,
> 
> p.s. The patches are based on top of
>      '[PATCH v2 0/4] OF GPIO integration for I2C/SPI GPIO chips'
>      http://lkml.org/lkml/2010/2/5/243
> 


-- 
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663
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