linux-kernel - Re: [PATCH 1/4] gpiolib: Introduce chip addition/removal notifier

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Date:	Tue, 26 Jan 2010 20:28:24 +0300
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bill Gatliff <bgat@...lgatliff.com>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] gpiolib: Introduce chip addition/removal notifier

On Mon, Jan 25, 2010 at 10:34:29PM -0800, David Brownell wrote:
> On Monday 25 January 2010, Anton Vorontsov wrote:
> > 
> > +config GPIOLIB_NOTIFIER
> > +       bool
> > +       help
> > +         This symbol is selected by subsystems that need to handle GPIO
> > +         chips addition and removal. E.g., this is used for the
> > +         OpenFirmware bindings.
> > +
> 
> I'm no huge fan of notifiers, but I suppose they have their place.
> 
> However ... I don't see a lot of win to making this optional.

OK, will remove it.

> Just
> inline the little two blocking_notifier_call_chain() calls directly,
> making this a *LOT* simpler.

I'd rather stay with gpio_call_chain() helper, it makes the code
a little bit prettier, IMO. Compare this:

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1103,6 +1107,9 @@ fail:
 		pr_err("gpiochip_add: gpios %d..%d (%s) not registered\n",
 			chip->base, chip->base + chip->ngpio - 1,
 			chip->label ? : "generic");
+	else
+		blocking_notifier_call_chain(&gpio_notifier,
+					     GPIO_NOTIFY_CHIP_ADDED, chip);
 	return status;
 }
 EXPORT_SYMBOL_GPL(gpiochip_add);
@@ -1119,6 +1126,13 @@ int gpiochip_remove(struct gpio_chip *chip)
 	int		status = 0;
 	unsigned	id;
 
+	/* Ask external subsystems to release the chip. */
+	status = blocking_notifier_call_chain(&gpio_notifier,
+					      GPIO_NOTIFY_CHIP_REMOVE, chip);
+	status = notifier_to_errno(status);
+	if (status)
+		return status;
+
 	spin_lock_irqsave(&gpio_lock, flags);
 
 	for (id = chip->base; id < chip->base + chip->ngpio; id++) {

--- 

With the call_chain helper:

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1029,6 +1030,16 @@ static inline void gpiochip_unexport(struct gpio_chip *chip)
 
 #endif /* CONFIG_GPIO_SYSFS */
 
+static int gpio_call_chain(struct gpio_chip *chip, enum gpio_notify_msg msg)
+{
+	int ret = blocking_notifier_call_chain(&gpio_notifier, msg, chip);
+
+	return notifier_to_errno(ret);
+}
+
 /**
  * gpiochip_add() - register a gpio_chip
  * @chip: the chip to register, with chip->base initialized
@@ -1103,6 +1114,9 @@ fail:
 		pr_err("gpiochip_add: gpios %d..%d (%s) not registered\n",
 			chip->base, chip->base + chip->ngpio - 1,
 			chip->label ? : "generic");
+	else
+		gpio_call_chain(chip, GPIO_NOTIFY_CHIP_ADDED);
+
 	return status;
 }
 EXPORT_SYMBOL_GPL(gpiochip_add);
@@ -1119,6 +1133,11 @@ int gpiochip_remove(struct gpio_chip *chip)
 	int		status = 0;
 	unsigned	id;
 
+	/* Ask external subsystems to release the chip. */
+	status = gpio_call_chain(chip, GPIO_NOTIFY_CHIP_REMOVE);
+	if (status)
+		return status;
+
 	spin_lock_irqsave(&gpio_lock, flags);
 
 	for (id = chip->base; id < chip->base + chip->ngpio; id++) {
--- 

Thanks!
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