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

[Janusz Krzysztofik]

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@xxxxxxxxx>
---
 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