From: a.hajda@samsung•com (Andrzej Hajda)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 2/2] gpio: gpiolib: set gpiochip_remove retval to void
Date: Tue, 10 Jun 2014 08:57:32 +0200 [thread overview]
Message-ID: <5396AC5C.2080108@samsung.com> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D17259A1F@AcuExch.aculab.com>
On 06/09/2014 03:43 PM, David Laight wrote:
> From: Of Andrzej Hajda
> ...
>>> You can't error out on module unload, although that's not really relevant
>>> here. gpiochip_remove() is typically called when the device that registered
>>> the GPIO chip is unbound. And despite some remove() callbacks having a
>>> return type of int you can not abort the removal of a device.
>>
>> It is a design flaw in many subsystems having providers and consumers,
>> not only GPIO. The same situation is with clock providers, regulators,
>> phys, drm_panels, ..., at least it was such last time I have tested it.
>>
>> The problem is that many frameworks assumes that lifetime of provider is
>> always bigger than lifetime of its consumers, and this is wrong
>> assumption - usually it is not possible to prevent unbinding driver from
>> device, so if the device is a provider there is no way to inform
>> consumers about his removal.
>>
>> Some solution for such problems is to use some kind of availability
>> callbacks for requesting resources (gpios, clocks, regulators,...)
>> instead of simple 'getters' (clk_get, gpiod_get). Callbacks should
>> guarantee that the resource is always valid between callback reporting
>> its availability and callback reporting its removal. Such approach seems
>> to be complicated at the first sight but it should allow to make the
>> code safe and as a bonus it will allow to avoid deferred probing.
>> Btw I have send already RFC for such framework [1].
>
> Callbacks for delete are generally a locking nightmare.
> A two-way handshake is also usually needed to avoid problems
> with concurrent disconnect requests.
The framework I have proposed is lock-less[1] and concurrent requests
are serialized so both objections are invalid.
[1]: in fact the framework uses spinlock, but only to protect internal
list simple operations, and even this could be converted to fully
lock-less implementation.
Andrzej
>
> David
>
next prev parent reply other threads:[~2014-06-10 6:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-29 21:54 [PATCH] gpio: removes all usage of gpiochip_remove retval abdoulaye berthe
2014-05-29 22:14 ` David Daney
[not found] ` <CABprBybQ-Jyk95zCqnoWjjyzhNyHVbsbEhb=vA5d=ZYp95_bFA@mail.gmail.com>
2014-05-29 23:40 ` Stephen Rothwell
2014-05-30 11:30 ` [PATCH 1/2] " abdoulaye berthe
2014-05-30 11:30 ` [PATCH 2/2] gpio: gpiolib: set gpiochip_remove retval to void abdoulaye berthe
2014-05-30 11:39 ` Geert Uytterhoeven
2014-05-30 15:48 ` Ralf Baechle
2014-05-30 17:33 ` David Daney
2014-05-30 18:16 ` Lars-Peter Clausen
2014-05-30 23:29 ` Greg KH
2014-05-31 7:35 ` Lars-Peter Clausen
2014-05-31 12:19 ` Dan Carpenter
2014-06-08 23:18 ` Ben Dooks
2014-06-09 11:29 ` Lars-Peter Clausen
2014-06-09 13:15 ` Andrzej Hajda
2014-06-09 13:43 ` David Laight
2014-06-10 6:57 ` Andrzej Hajda [this message]
2014-05-29 23:25 ` [PATCH] gpio: removes all usage of gpiochip_remove retval Greg KH
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