From: Bartosz Golaszewski <[email protected]>
GPIO descriptors are freed by consumers using gpiod_put(). The name of
this function suggests some reference counting is going on but it's not
true.
Use kref to actually introduce reference counting for gpio_desc objects.
Add a corresponding gpiod_get() helper for increasing the reference count.
This doesn't change anything for already existing (correct) drivers but
allows us to keep track of GPIO descs used by multiple users.
Signed-off-by: Bartosz Golaszewski <[email protected]>
---
drivers/gpio/gpiolib.c | 38 +++++++++++++++++++++++++++++++----
drivers/gpio/gpiolib.h | 1 +
include/linux/gpio/consumer.h | 1 +
3 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index da8ffd40aa97..a00e28ca8a49 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2798,6 +2798,8 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
goto done;
}
+ kref_init(&desc->ref);
+
if (chip->request) {
/* chip->request may sleep */
spin_unlock_irqrestore(&gpio_lock, flags);
@@ -2941,6 +2943,13 @@ void gpiod_free(struct gpio_desc *desc)
}
}
+static void gpiod_free_kref(struct kref *ref)
+{
+ struct gpio_desc *desc = container_of(ref, struct gpio_desc, ref);
+
+ gpiod_free(desc);
+}
+
/**
* gpiochip_is_requested - return string iff signal was requested
* @chip: controller managing the signal
@@ -5075,18 +5084,39 @@ struct gpio_descs *__must_check gpiod_get_array_optional(struct device *dev,
EXPORT_SYMBOL_GPL(gpiod_get_array_optional);
/**
- * gpiod_put - dispose of a GPIO descriptor
- * @desc: GPIO descriptor to dispose of
+ * gpiod_put - decrease the reference count of a GPIO descriptor
+ * @desc: GPIO descriptor to unref
*
* No descriptor can be used after gpiod_put() has been called on it.
*/
void gpiod_put(struct gpio_desc *desc)
{
- if (desc)
- gpiod_free(desc);
+ VALIDATE_DESC_VOID(desc);
+
+ kref_put(&desc->ref, gpiod_free_kref);
}
EXPORT_SYMBOL_GPL(gpiod_put);
+/**
+ * gpiod_ref - increase the reference count of a GPIO descriptor
+ * @desc: GPIO descriptor to reference
+ *
+ * Returns the same gpio_desc after increasing the reference count.
+ */
+struct gpio_desc *gpiod_ref(struct gpio_desc *desc)
+{
+ VALIDATE_DESC_PTR(desc);
+
+ if (!test_bit(FLAG_REQUESTED, &desc->flags)) {
+ pr_warn("gpiolib: unable to increase the reference count of unrequested GPIO descriptor\n");
+ return desc;
+ }
+
+ kref_get(&desc->ref);
+ return desc;
+}
+EXPORT_SYMBOL_GPL(gpiod_ref);
+
/**
* gpiod_put_array - dispose of multiple GPIO descriptors
* @descs: struct gpio_descs containing an array of descriptors
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 3e0aab2945d8..51a92c43dd55 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -119,6 +119,7 @@ struct gpio_desc {
const char *label;
/* Name of the GPIO */
const char *name;
+ struct kref ref;
};
int gpiod_request(struct gpio_desc *desc, const char *label);
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index bf2d017dd7b7..c7b5fb3d9d64 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -81,6 +81,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
struct gpio_descs *__must_check gpiod_get_array_optional(struct device *dev,
const char *con_id,
enum gpiod_flags flags);
+struct gpio_desc *gpiod_ref(struct gpio_desc *desc);
void gpiod_put(struct gpio_desc *desc);
void gpiod_put_array(struct gpio_descs *descs);
--
2.25.0
On Fri, Feb 21, 2020 at 4:48 PM Bartosz Golaszewski <[email protected]> wrote:
> From: Bartosz Golaszewski <[email protected]>
>
> GPIO descriptors are freed by consumers using gpiod_put(). The name of
> this function suggests some reference counting is going on but it's not
> true.
>
> Use kref to actually introduce reference counting for gpio_desc objects.
> Add a corresponding gpiod_get() helper for increasing the reference count.
>
> This doesn't change anything for already existing (correct) drivers but
> allows us to keep track of GPIO descs used by multiple users.
>
> Signed-off-by: Bartosz Golaszewski <[email protected]>
I'm having some trouble figuring out if we might be reinventing
a wheel here.
A while back there was a proposed patch to add device links
between GPIO producers and consumers, so that a GPIO
chip won't be dropped while there are active consumers.
(I don't remember who sent the patch.)
We have a similar functionality in pin control if the
.link_consumers property is set on the pincontrol device.
I was thinking about making that compulsory at one point.
The device links use a kref already existing in struct
device and would in this case be the kref in the struct
device for the struct gpio_device.
So if that existed, gpiod_ref could just grab another
device_link_add().
Maybe we should just add device links between all
GPIO consumers (devices) and struct gpio_device:s
struct device and implement it like this so we don't
have to back out of this later?
C.f. commit
commit 036f394dd77f8117346874151793ec38967d843f
pinctrl: Enable device link creation for pin control
(...)
> @@ -81,6 +81,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
> struct gpio_descs *__must_check gpiod_get_array_optional(struct device *dev,
> const char *con_id,
> enum gpiod_flags flags);
> +struct gpio_desc *gpiod_ref(struct gpio_desc *desc);
> void gpiod_put(struct gpio_desc *desc);
> void gpiod_put_array(struct gpio_descs *descs);
You forgot to add a stub for the case where GPIOLIB is not
compiled in I think? (Lower in the same file.)
Yours,
Linus Walleij
pt., 28 lut 2020 o 23:33 Linus Walleij <[email protected]> napisał(a):
>
> On Fri, Feb 21, 2020 at 4:48 PM Bartosz Golaszewski <[email protected]> wrote:
>
> > From: Bartosz Golaszewski <[email protected]>
> >
> > GPIO descriptors are freed by consumers using gpiod_put(). The name of
> > this function suggests some reference counting is going on but it's not
> > true.
> >
> > Use kref to actually introduce reference counting for gpio_desc objects.
> > Add a corresponding gpiod_get() helper for increasing the reference count.
> >
> > This doesn't change anything for already existing (correct) drivers but
> > allows us to keep track of GPIO descs used by multiple users.
> >
> > Signed-off-by: Bartosz Golaszewski <[email protected]>
>
> I'm having some trouble figuring out if we might be reinventing
> a wheel here.
>
> A while back there was a proposed patch to add device links
> between GPIO producers and consumers, so that a GPIO
> chip won't be dropped while there are active consumers.
>
> (I don't remember who sent the patch.)
>
> We have a similar functionality in pin control if the
> .link_consumers property is set on the pincontrol device.
> I was thinking about making that compulsory at one point.
>
> The device links use a kref already existing in struct
> device and would in this case be the kref in the struct
> device for the struct gpio_device.
>
> So if that existed, gpiod_ref could just grab another
> device_link_add().
>
I was always under the impression that device links are aimed mostly
at runtime PM.
> Maybe we should just add device links between all
> GPIO consumers (devices) and struct gpio_device:s
> struct device and implement it like this so we don't
> have to back out of this later?
>
> C.f. commit
> commit 036f394dd77f8117346874151793ec38967d843f
> pinctrl: Enable device link creation for pin control
>
Yes, definitely looks like it's done with PM in mind. Maybe we should
do what nvmem does? Define a struct device_type for GPIO chips with an
appropriate release() callback and use get_device() and put_device()?
Although nvmem seems to use kref for cells and device reference
counting somewhat separately - maybe that's something to address too.
> (...)
> > @@ -81,6 +81,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
> > struct gpio_descs *__must_check gpiod_get_array_optional(struct device *dev,
> > const char *con_id,
> > enum gpiod_flags flags);
> > +struct gpio_desc *gpiod_ref(struct gpio_desc *desc);
> > void gpiod_put(struct gpio_desc *desc);
> > void gpiod_put_array(struct gpio_descs *descs);
>
> You forgot to add a stub for the case where GPIOLIB is not
> compiled in I think? (Lower in the same file.)
>
> Yours,
> Linus Walleij
Yeah this is fixed in the next version (with a different subject since
it no longer concerns nvmem that much).
Bart