linux-kernel - Re: [PATCH] gpio: better lookup method for platform GPIOs

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Date:	Mon, 2 Dec 2013 13:11:24 +0200
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Rhyland Klein <rklein@...dia.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: better lookup method for platform GPIOs

Hi,

On Mon, Dec 02, 2013 at 07:33:35PM +0900, Alex Courbot wrote:
> On 11/29/2013 08:57 PM, Heikki Krogerus wrote:
> >Hi,
> >
> >On Thu, Nov 28, 2013 at 05:46:28PM +0900, Alexandre Courbot wrote:
> >>@@ -88,16 +89,20 @@ Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
> >>
> >>  A lookup table can then be defined as follows:
> >>
> >>-	struct gpiod_lookup gpios_table[] = {
> >>-	GPIO_LOOKUP_IDX("gpio.0", 15, "foo.0", "led", 0, GPIO_ACTIVE_HIGH),
> >>-	GPIO_LOOKUP_IDX("gpio.0", 16, "foo.0", "led", 1, GPIO_ACTIVE_HIGH),
> >>-	GPIO_LOOKUP_IDX("gpio.0", 17, "foo.0", "led", 2, GPIO_ACTIVE_HIGH),
> >>-	GPIO_LOOKUP("gpio.0", 1, "foo.0", "power", GPIO_ACTIVE_LOW),
> >>-	};
> >>+struct gpiod_lookup_table gpios_table = {
> >>+	.dev_id = "foo.0",
> >>+	.size = 4,
> >>+	.table = {
> >>+	GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
> >>+	GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
> >>+	GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
> >>+	GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
> >>+	},
> >>+};
> >
> >Instead of using the size variable, wouldn't it be more clear to
> >expect the array to be null terminated?
> 
> This is a zero-length array, its entries are not pointers but
> flattened lookup entries. Thus you cannot simply null-terminate it.
> It would be possible to use { NULL } as a terminator, but this would
> expand into a whole gpiod_lookup and is not very pleasant
> esthetically-speaking. So I think the size member is maybe better
> suited here.

The gpio_loopup_table would look like this, which IMO is more nicer
looking compared to the extra size variable:

struct gpiod_lookup_table gpios_table = {
	.dev_id = "foo.0",
	.table = {
        	GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
	        GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
        	GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
	        GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
                { },
	},
};

That would also make it more straight forward to handle in gbiolib.c:

struct gpiod_lookup *p;
...
for (p = table->table; p->chip_label; p++) {
...

Thanks,

-- 
heikki
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