[RFC PATCH v2 09/12] gpiolib: Identify GPIO descriptor arrays with direct mapping

Janusz Krzysztofik
2018-08-06T22:29:46Z

Certain GPIO array lookup results may map directly to GPIO pins of a
single GPIO chip in hardware order. If that condition is recognized
and handled efficiently, significant performance gain of get/set array
functions may be possible.

While processing a request for an array of GPIO descriptors, verify if
the descriptors just collected represent consecutive pins of a single
GPIO chip. Pass that information with the array to the caller so it
can benefit from enhanced performance as soon as bitmap based get/set
array functions which can make efficient use of that are available.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
---
Documentation/driver-api/gpio/consumer.rst | 4 +++-
drivers/gpio/gpiolib.c | 14 ++++++++++++++
include/linux/gpio/consumer.h | 1 +
3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst
index aa03f389d41d..38a990b5f3b6 100644
--- a/Documentation/driver-api/gpio/consumer.rst
+++ b/Documentation/driver-api/gpio/consumer.rst
@@ -109,11 +109,13 @@ For a function using multiple GPIOs all of those can be obtained with one call::
enum gpiod_flags flags)

This function returns a struct gpio_descs which contains an array of
-descriptors::
+descriptors. It may also contain a valid descriptor of a single GPIO chip in
+case the array strictly matches pin hardware layout of the chip::

struct gpio_descs {
unsigned int ndescs;
struct gpio_desc *desc[];
+ struct gpio_chip *chip;
}

The following function returns NULL instead of -ENOENT if no GPIOs have been
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index bdbfc95793e7..c50bcec6e2d7 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4161,6 +4161,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
{
struct gpio_desc *desc;
struct gpio_descs *descs;
+ struct gpio_chip *chip;
int count;

count = gpiod_count(dev, con_id);
@@ -4177,6 +4178,19 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
gpiod_put_array(descs);
return ERR_CAST(desc);
}
+
+ /*
+ * Verify if the array qualifies for fast bitmap operations
+ * (single chip, pins in hardware order starting from 0)
+ * and mark the array with the chip descriptor if true.
+ */
+ chip = gpiod_to_chip(desc);
+ if (descs->chip == NULL)
+ descs->chip = chip;
+ if (!IS_ERR(descs->chip) && (chip != descs->chip ||
+ gpio_chip_hwgpio(desc) != descs->ndescs))
+ descs->chip = ERR_PTR(-EINVAL);
+
descs->desc[descs->ndescs] = desc;
descs->ndescs++;
}
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index 21ddbe440030..862ee027a02f 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -22,6 +22,7 @@ struct gpio_desc;
* gpiod_get_array().
*/
struct gpio_descs {
+ struct gpio_chip *chip;
unsigned int ndescs;
struct gpio_desc *desc[];
};
--
2.16.4