[PATCH v7-fix] gpio: Add driver for basic memory-mapped GPIO controllers (fix)

[Anton Vorontsov <cbouatmailru@gmail.com>]

On Fri, Sep 24, 2010 at 02:45:35PM -0700, Andrew Morton wrote:
> It would be good to document `bits' and `big_endian_bits', and to
> describe what `lock' locks.

Done.

> > +static int bgpio_dir_in(struct gpio_chip *gc, unsigned int gpio)
> > +{
> > +	return 0;
> > +}
> 
> hm, what does this mean.  The hardware cannot set pin directions to
> "in"?

Nope, 0 is the success. The hardware cannot set pin directions
at all (well, some hw can, but we don't support these yet).

> > +	return gpiochip_add(&bgc->gc);
> > +}
> 
> If this function returns -EINVAL then much head-scratching will ensue. 
> It might make your life easier to emit a diagnostic just before the
> failure so you can work out why it failed.

OK.

Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>
---

Thanks!

 drivers/gpio/basic_mmio_gpio.c |   22 +++++++++++++++++++---
 1 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/gpio/basic_mmio_gpio.c b/drivers/gpio/basic_mmio_gpio.c
index c2c11e7..3addea6 100644
--- a/drivers/gpio/basic_mmio_gpio.c
+++ b/drivers/gpio/basic_mmio_gpio.c
@@ -66,12 +66,23 @@ struct bgpio_chip {
 	void __iomem *reg_dat;
 	void __iomem *reg_set;
 	void __iomem *reg_clr;
-	spinlock_t lock;
 
+	/* Number of bits (GPIOs): <register width> * 8. */
 	int bits;
+
+	/*
+	 * Some GPIO controllers work with the big-endian bits notation,
+	 * e.g. in a 8-bits register, GPIO7 is the least significant bit.
+	 */
 	int big_endian_bits;
 
-	/* shadowed data register to clear/set bits safely */
+	/*
+	 * Used to lock bgpio_chip->data. Also, this is needed to keep
+	 * shadowed and real data registers writes together.
+	 */
+	spinlock_t lock;
+
+	/* Shadowed data register to clear/set bits safely. */
 	unsigned long data;
 };
 
@@ -181,6 +192,7 @@ static int __devinit bgpio_probe(struct platform_device *pdev)
 	struct resource *res_clr;
 	resource_size_t dat_sz;
 	int bits;
+	int ret;
 
 	res_dat = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dat");
 	if (!res_dat)
@@ -238,7 +250,11 @@ static int __devinit bgpio_probe(struct platform_device *pdev)
 
 	dev_set_drvdata(dev, bgc);
 
-	return gpiochip_add(&bgc->gc);
+	ret = gpiochip_add(&bgc->gc);
+	if (ret)
+		dev_err(dev, "gpiochip_add() failed: %d\n", ret);
+
+	return ret;
 }
 
 static int __devexit bgpio_remove(struct platform_device *pdev)
-- 
1.7.0.5