linux-kernel - Re: [PATCH v2 1/5] gpiolib: Allow GPIO chips to request their own GPIOs

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Date:	Thu, 13 Mar 2014 13:46:15 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lan Tianyu <tianyu.lan@...el.com>,
	Lv Zheng <lv.zheng@...el.com>, Alan Cox <alan.cox@...el.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] gpiolib: Allow GPIO chips to request their own GPIOs

On Mon, Mar 10, 2014 at 9:54 PM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> Sometimes it is useful to allow GPIO chips themselves to request GPIOs they
> own through gpiolib API. One use case is ACPI ASL code that should be able
> to toggle GPIOs through GPIO operation regions.
>
> We can't use gpio_request() because it will pin the module to the kernel
> forever (it calls try_module_get()). To solve this we move module refcount
> manipulation to gpiod_request() and let __gpiod_request() handle the actual
> request. This changes the sequence a bit as now try_module_get() is called
> outside of gpio_lock (I think this is safe, try_module_get() handles
> serialization it needs already).
>
> Then we provide gpiolib internal functions gpiochip_request/free_own_desc()
> that do the same as gpio_request() but don't manipulate module refrence
> count. This allows the GPIO chip driver to request and free descriptors it
> owns without being pinned to the kernel forever.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

Reviewed-by: Alexandre Courbot <acourbot@...dia.com>

The change is clear and does not add too much complexity to the code,
so no reason to oppose it.
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