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Date: Wed, 05 Dec 2012 20:01:07 +0100
From: Wolfgang Grandegger <wg@...ndegger.com>
To: Roland Stigge <stigge@...com.de>
CC: gregkh@...uxfoundation.org, grant.likely@...retlab.ca,
linus.walleij@...aro.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, w.sang@...gutronix.de,
jbe@...gutronix.de, plagnioj@...osoft.com, highguy@...il.com,
broonie@...nsource.wolfsonmicro.com, daniel-gl@....net,
rmallon@...il.com, tru@...k-microwave.de, sr@...x.de
Subject: Re: [PATCH 3/6 v9] gpio: Add userland device interface to block GPIO
On 12/04/2012 09:39 PM, Roland Stigge wrote:
> This patch adds a character device interface to the block GPIO system.
>
> Signed-off-by: Roland Stigge <stigge@...com.de>
> ---
> Documentation/ABI/testing/dev-gpioblock | 34 +++++
> drivers/gpio/gpiolib.c | 208 +++++++++++++++++++++++++++++++-
> include/linux/gpio.h | 10 +
> 3 files changed, 251 insertions(+), 1 deletion(-)
>
> --- /dev/null
> +++ linux-2.6/Documentation/ABI/testing/dev-gpioblock
> @@ -0,0 +1,34 @@
> +What: /dev/<gpioblock>
> +Date: Nov 2012
> +KernelVersion: 3.7
> +Contact: Roland Stigge <stigge@...com.de>
> +Description: The /dev/<gpioblock> character device node provides userspace
> + access to GPIO blocks, named exactly as the block, e.g.
> + /dev/block0.
> +
> + Reading:
> + When reading sizeof(unsigned long) bytes from the device, the
> + current state of the block, masked by the current mask (see
> + below) can be obtained as a word. When the device is opened
> + with O_NONBLOCK, read() always returns with data immediately,
> + otherwise it blocks until data is available, see IRQ handling
> + below.
> +
> + Writing:
> + By writing sizeof(unsigned long) bytes to the device, the
> + current state of the block can be set. This operation is
> + masked by the current mask (see below).
> +
> + IRQ handling:
> + When one or more IRQs in the block are IRQ capable, you can
> + poll() on the device to check/wait for this IRQ. If no IRQ
> + is available, poll() returns -ENOSYS and userspace needs to
> + (busy) poll itself if necessary.
> +
> + Setting the mask (default: all bits set):
> + By doing an ioctl(fd, 0, &mask) with an unsigned long mask, the
> + current mask for read and write operations on this gpio block
> + can be set.
> +
> + See also Documentation/gpio.txt for an explanation of block
> + GPIO.
> --- linux-2.6.orig/drivers/gpio/gpiolib.c
> +++ linux-2.6/drivers/gpio/gpiolib.c
> @@ -11,6 +11,8 @@
> #include <linux/of_gpio.h>
> #include <linux/idr.h>
> #include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/poll.h>
>
> #define CREATE_TRACE_POINTS
> #include <trace/events/gpio.h>
> @@ -2122,6 +2124,190 @@ struct gpio_block *gpio_block_find_by_na
> }
> EXPORT_SYMBOL_GPL(gpio_block_find_by_name);
>
> +static struct gpio_block *gpio_block_find_by_minor(int minor)
> +{
> + struct gpio_block *i;
> +
> + list_for_each_entry(i, &gpio_block_list, list)
> + if (i->miscdev.minor == minor)
> + return i;
> + return NULL;
> +}
> +
> +static bool gpio_block_is_irq_duplicate(struct gpio_block *block, int index)
> +{
> + int irq = gpio_to_irq(block->gpio[index]);
> + int i;
> +
> + for (i = 0; i < index; i++)
> + if (gpio_to_irq(block->gpio[i]) == irq)
> + return true;
> + return false;
> +}
> +
> +static irqreturn_t gpio_block_irq_handler(int irq, void *dev)
> +{
> + struct gpio_block *block = dev;
> +
> + wake_up_interruptible(&block->wait_queue);
> + block->got_int = true;
> +
> + return IRQ_HANDLED;
> +}
> +
> +static int gpio_block_fop_open(struct inode *in, struct file *f)
> +{
> + int i;
> + struct gpio_block *block = gpio_block_find_by_minor(MINOR(in->i_rdev));
> + int status;
> + int irq;
> +
> + if (!block)
> + return -ENOENT;
> +
> + block->irq_controlled = false;
> + block->got_int = false;
> + init_waitqueue_head(&block->wait_queue);
> + f->private_data = block;
> +
> + for (i = 0; i < block->ngpio; i++) {
> + status = gpio_request(block->gpio[i], "gpioblock dev");
You could use the name of the GPIO block.
> + if (status)
> + goto err1;
> +
> + irq = gpio_to_irq(block->gpio[i]);
> + if (irq >= 0 &&
> + !test_bit(FLAG_IS_OUT, &gpio_desc[block->gpio[i]].flags) &&
> + !gpio_block_is_irq_duplicate(block, i)) {
> + status = request_irq(irq, gpio_block_irq_handler,
> + IRQF_TRIGGER_FALLING,
> + block->name, block);
> + if (status)
> + goto err2;
> +
> + block->irq_controlled = true;
> + }
> + }
There is no need to request IRQs if "O_NONBLOCK" is specified.
> +
> + return 0;
> +
> +err1:
> + while (i > 0) {
> + i--;
> +
> + irq = gpio_to_irq(block->gpio[i]);
> + if (irq >= 0 &&
> + !test_bit(FLAG_IS_OUT, &gpio_desc[block->gpio[i]].flags) &&
> + !gpio_block_is_irq_duplicate(block, i))
> + free_irq(irq, block);
> +err2:
> + gpio_free(block->gpio[i]);
> + }
> + return status;
> +}
> +
> +static int gpio_block_fop_release(struct inode *in, struct file *f)
> +{
> + int i;
> + struct gpio_block *block = (struct gpio_block *)f->private_data;
> +
> + for (i = 0; i < block->ngpio; i++) {
> + int irq = gpio_to_irq(block->gpio[i]);
> +
> + if (irq >= 0 &&
> + !test_bit(FLAG_IS_OUT, &gpio_desc[block->gpio[i]].flags) &&
> + !gpio_block_is_irq_duplicate(block, i))
> + free_irq(irq, block);
> +
> + gpio_free(block->gpio[i]);
> + }
> +
> + return 0;
> +}
> +
> +static ssize_t gpio_block_fop_read(struct file *f, char __user *buf, size_t n,
> + loff_t *offset)
> +{
> + struct gpio_block *block = (struct gpio_block *)f->private_data;
> + int err;
> +
> + if (block->irq_controlled) {
> + if (!(f->f_flags & O_NONBLOCK))
> + wait_event_interruptible(block->wait_queue,
> + block->got_int);
> + block->got_int = 0;
> + }
> +
> + if (n >= sizeof(unsigned long)) {
> + unsigned long values = gpio_block_get(block, block->cur_mask);
> +
> + err = put_user(values, (unsigned long __user *)buf);
> + if (err)
> + return err;
> +
> + return sizeof(unsigned long);
> + }
> + return 0;
> +}
I observed that the read returns once immediately (without blocking)
after reboot. I did not look into that yet.
Wolfgang.
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