[v4,03/11] gpiolib: provide gpio_device_find()
Commit Message
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
gpiochip_find() is wrong and its kernel doc is misleading as the
function doesn't return a reference to the gpio_chip but just a raw
pointer. The chip itself is not guaranteed to stay alive, in fact it can
be deleted at any point. Also: other than GPIO drivers themselves,
nobody else has any business accessing gpio_chip structs.
Provide a new gpio_device_find() function that returns a real reference
to the opaque gpio_device structure that is guaranteed to stay alive for
as long as there are active users of it.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
drivers/gpio/gpiolib.c | 71 +++++++++++++++++++++++++++----------
include/linux/gpio/driver.h | 3 ++
2 files changed, 56 insertions(+), 18 deletions(-)
Comments
On Wed, Sep 27, 2023 at 04:29:23PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> gpiochip_find() is wrong and its kernel doc is misleading as the
> function doesn't return a reference to the gpio_chip but just a raw
> pointer. The chip itself is not guaranteed to stay alive, in fact it can
> be deleted at any point. Also: other than GPIO drivers themselves,
> nobody else has any business accessing gpio_chip structs.
>
> Provide a new gpio_device_find() function that returns a real reference
> to the opaque gpio_device structure that is guaranteed to stay alive for
> as long as there are active users of it.
...
> struct gpio_chip *gpiochip_find(void *data,
> int (*match)(struct gpio_chip *gc,
> +struct gpio_device *gpio_device_find(void *data,
> + int (*match)(struct gpio_chip *gc,
> + void *data))
Why not
typedef int (*gpio_chip_match_fn)(struct gpio_chip *gc, void *data);
?
On Mon, Oct 2, 2023 at 11:42 AM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Wed, Sep 27, 2023 at 04:29:23PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> >
> > gpiochip_find() is wrong and its kernel doc is misleading as the
> > function doesn't return a reference to the gpio_chip but just a raw
> > pointer. The chip itself is not guaranteed to stay alive, in fact it can
> > be deleted at any point. Also: other than GPIO drivers themselves,
> > nobody else has any business accessing gpio_chip structs.
> >
> > Provide a new gpio_device_find() function that returns a real reference
> > to the opaque gpio_device structure that is guaranteed to stay alive for
> > as long as there are active users of it.
>
> ...
>
> > struct gpio_chip *gpiochip_find(void *data,
> > int (*match)(struct gpio_chip *gc,
>
> > +struct gpio_device *gpio_device_find(void *data,
> > + int (*match)(struct gpio_chip *gc,
> > + void *data))
>
> Why not
>
> typedef int (*gpio_chip_match_fn)(struct gpio_chip *gc, void *data);
>
Because gpiochip_find() will go away as soon as we convert all users.
Bart
> ?
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
On Mon, Oct 02, 2023 at 11:52:52AM +0200, Bartosz Golaszewski wrote:
> On Mon, Oct 2, 2023 at 11:42 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Wed, Sep 27, 2023 at 04:29:23PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
...
> > > struct gpio_chip *gpiochip_find(void *data,
> > > int (*match)(struct gpio_chip *gc,
> >
> > > +struct gpio_device *gpio_device_find(void *data,
> > > + int (*match)(struct gpio_chip *gc,
> > > + void *data))
> >
> > Why not
> >
> > typedef int (*gpio_chip_match_fn)(struct gpio_chip *gc, void *data);
>
> Because gpiochip_find() will go away as soon as we convert all users.
And gpio_device_find() does not. So, I didn't get this argument.
On Mon, Oct 2, 2023 at 11:57 AM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Mon, Oct 02, 2023 at 11:52:52AM +0200, Bartosz Golaszewski wrote:
> > On Mon, Oct 2, 2023 at 11:42 AM Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
> > > On Wed, Sep 27, 2023 at 04:29:23PM +0200, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> ...
>
> > > > struct gpio_chip *gpiochip_find(void *data,
> > > > int (*match)(struct gpio_chip *gc,
> > >
> > > > +struct gpio_device *gpio_device_find(void *data,
> > > > + int (*match)(struct gpio_chip *gc,
> > > > + void *data))
> > >
> > > Why not
> > >
> > > typedef int (*gpio_chip_match_fn)(struct gpio_chip *gc, void *data);
> >
> > Because gpiochip_find() will go away as soon as we convert all users.
>
> And gpio_device_find() does not. So, I didn't get this argument.
>
This symbol would only be used in a single place. But whatever, I can
do it as there will be another respin anyway.
Bart
@@ -1014,16 +1014,10 @@ void gpiochip_remove(struct gpio_chip *gc)
}
EXPORT_SYMBOL_GPL(gpiochip_remove);
-/**
- * gpiochip_find() - iterator for locating a specific gpio_chip
- * @data: data to pass to match function
- * @match: Callback function to check gpio_chip
+/*
+ * FIXME: This will be removed soon.
*
- * Similar to bus_find_device. It returns a reference to a gpio_chip as
- * determined by a user supplied @match callback. The callback should return
- * 0 if the device doesn't match and non-zero if it does. If the callback is
- * non-zero, this function will return to the caller and not iterate over any
- * more gpio_chips.
+ * This function is depracated, don't use.
*/
struct gpio_chip *gpiochip_find(void *data,
int (*match)(struct gpio_chip *gc,
@@ -1031,21 +1025,62 @@ struct gpio_chip *gpiochip_find(void *data,
{
struct gpio_device *gdev;
struct gpio_chip *gc = NULL;
- unsigned long flags;
- spin_lock_irqsave(&gpio_lock, flags);
- list_for_each_entry(gdev, &gpio_devices, list)
- if (gdev->chip && match(gdev->chip, data)) {
- gc = gdev->chip;
- break;
- }
-
- spin_unlock_irqrestore(&gpio_lock, flags);
+ gdev = gpio_device_find(data, match);
+ if (gdev) {
+ gc = gdev->chip;
+ gpio_device_put(gdev);
+ }
return gc;
}
EXPORT_SYMBOL_GPL(gpiochip_find);
+/**
+ * gpio_device_find() - find a specific GPIO device
+ * @data: data to pass to match function
+ * @match: Callback function to check gpio_chip
+ *
+ * Returns:
+ * New reference to struct gpio_device.
+ *
+ * Similar to bus_find_device(). It returns a reference to a gpio_device as
+ * determined by a user supplied @match callback. The callback should return
+ * 0 if the device doesn't match and non-zero if it does. If the callback
+ * returns non-zero, this function will return to the caller and not iterate
+ * over any more gpio_devices.
+ *
+ * The callback takes the GPIO chip structure as argument. During the execution
+ * of the callback function the chip is protected from being freed. TODO: This
+ * actually has yet to be implemented.
+ *
+ * If the function returns non-NULL, the returned reference must be freed by
+ * the caller using gpio_device_put().
+ */
+struct gpio_device *gpio_device_find(void *data,
+ int (*match)(struct gpio_chip *gc,
+ void *data))
+{
+ struct gpio_device *gdev;
+
+ /*
+ * Not yet but in the future the spinlock below will become a mutex.
+ * Annotate this function before anyone tries to use it in interrupt
+ * context like it happened with gpiochip_find().
+ */
+ might_sleep();
+
+ guard(spinlock_irqsave)(&gpio_lock);
+
+ list_for_each_entry(gdev, &gpio_devices, list) {
+ if (gdev->chip && match(gdev->chip, data))
+ return gpio_device_get(gdev);
+ }
+
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(gpio_device_find);
+
static int gpiochip_match_name(struct gpio_chip *gc, void *data)
{
const char *name = data;
@@ -608,6 +608,9 @@ int devm_gpiochip_add_data_with_key(struct device *dev, struct gpio_chip *gc,
struct gpio_chip *gpiochip_find(void *data,
int (*match)(struct gpio_chip *gc, void *data));
+struct gpio_device *gpio_device_find(void *data,
+ int (*match)(struct gpio_chip *gc, void *data));
+
struct gpio_device *gpio_device_get(struct gpio_device *gdev);
void gpio_device_put(struct gpio_device *gdev);