Messages in this thread |  | | Date | Wed, 5 Mar 2014 14:05:50 +0200 | From | Mika Westerberg <> | Subject | Re: [PATCH 1/6] gpiolib: Allow GPIO chips to request their own GPIOs |
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On Wed, Mar 05, 2014 at 10:49:41AM +0800, Linus Walleij wrote: > On Tue, Feb 25, 2014 at 12:00 AM, Mika Westerberg > <mika.westerberg@linux.intel.com> wrote: > > > Sometimes it is useful to allow GPIO chips themselves to request GPIOs they > > own through gpiolib API. One usecase is ACPI ASL code that should be able > > to toggle GPIOs through GPIO operation regions. > > > > We can't really use gpio_request() and its counterparts because it will pin > > the module to the kernel forever (as it calls module_get()). Instead we > > provide a gpiolib internal functions gpiochip_request/free_own_desc() that > > work the same as gpio_request() but don't manipulate module refrence count. > > > > Since it's the GPIO chip driver who requests the GPIOs in the first place > > we can be sure that it cannot be unloaded without the driver knowing about > > that. Furthermore we only limit this functionality to be available only > > inside gpiolib. > > > > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com> > > I fully trust you in doing the ACPI stuff in patches 2-n but on this patch > in particular I want Alexandre's review tag as well, as he's working > actively with the descriptor API and I don't want to add too many quirks > without his consent.
Thanks for your trust :)
> So Alexandre, what do you say about this?
I'm about to send v2 of the series with Rafael's comments taken into account. However, I stumbled to another locking problem:
I'm going to move taking the gpio_lock outside of __gpiod_request() and have __gpiod_request() to release that lock, so that we can call chip->request() safely.
Since we are using _irqsave()/_irqrestore() versions, it means that I need to pass flags as a pointer from gpiod_request() to __gpiod_request() like:
spin_lock_irqsave(&gpio_lock, flags); if (try_module_get(chip->owner)) { ret = __gpiod_request(desc, label, &flags); ...
Is that acceptable or can you guys suggest some alternative? One alternative that I can think about is to have __gpiod_request() to take the lock and move try_module_get() outside to gpiod_request():
__gpiod_request() { unsigned long flags;
spin_lock_irqsave(&gpio_lock, flags); ... }
gpiod_request(): { ... if (try_module_get(chip->owner)) { ret = __gpiod_request(desc, label); ... }
Thoughts?
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