[PATCH v6 2/4] gpiolib: Identify arrays matching GPIO hardware

Janusz Krzysztofik
2018-08-31T22:56:03Z

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, identify
those which represent corresponding pins of a single GPIO chip. Skip
over pins which require open source or open drain special processing.
Moreover, identify pins which require inversion. Pass a pointer to
that information with the array to the caller so it can benefit from
enhanced performance as soon as get/set array functions can accept and
make efficient use of it.

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
---
Documentation/driver-api/gpio/consumer.rst | 4 +-
drivers/gpio/gpiolib.c | 72 +++++++++++++++++++++++++++++-
drivers/gpio/gpiolib.h | 9 ++++
include/linux/gpio/consumer.h | 9 ++++
4 files changed, 92 insertions(+), 2 deletions(-)

diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst
index ed68042ddccf..7e0298b9a7b9 100644
--- a/Documentation/driver-api/gpio/consumer.rst
+++ b/Documentation/driver-api/gpio/consumer.rst
@@ -109,9 +109,11 @@ 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 also contains a pointer to a gpiolib private structure which,
+if passed back to get/set array functions, may speed up I/O proocessing::

struct gpio_descs {
+ struct gpio_array *info;
unsigned int ndescs;
struct gpio_desc *desc[];
}
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index f0e9ffa8cab6..c1ed1c759345 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4174,7 +4174,9 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
{
struct gpio_desc *desc;
struct gpio_descs *descs;
- int count;
+ struct gpio_array *array_info = NULL;
+ struct gpio_chip *chip;
+ int count, bitmap_size;

count = gpiod_count(dev, con_id);
if (count < 0)
@@ -4190,9 +4192,77 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
gpiod_put_array(descs);
return ERR_CAST(desc);
}
+
descs->desc[descs->ndescs] = desc;
+
+ chip = gpiod_to_chip(desc);
+ /*
+ * Select a chip of first array member
+ * whose index matches its pin hardware number
+ * as a candidate for fast bitmap processing.
+ */
+ if (!array_info && gpio_chip_hwgpio(desc) == descs->ndescs) {
+ struct gpio_descs *array;
+
+ bitmap_size = BITS_TO_LONGS(chip->ngpio > count ?
+ chip->ngpio : count);
+
+ array = kzalloc(struct_size(descs, desc, count) +
+ struct_size(array_info, invert_mask,
+ 3 * bitmap_size), GFP_KERNEL);
+ if (!array) {
+ gpiod_put_array(descs);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ memcpy(array, descs,
+ struct_size(descs, desc, descs->ndescs + 1));
+ kfree(descs);
+
+ descs = array;
+ array_info = (void *)(descs->desc + count);
+ array_info->get_mask = array_info->invert_mask +
+ bitmap_size;
+ array_info->set_mask = array_info->get_mask +
+ bitmap_size;
+
+ array_info->desc = descs->desc;
+ array_info->size = count;
+ array_info->chip = chip;
+ bitmap_set(array_info->get_mask, descs->ndescs,
+ count - descs->ndescs);
+ bitmap_set(array_info->set_mask, descs->ndescs,
+ count - descs->ndescs);
+ descs->info = array_info;
+ }
+ /*
+ * Unmark members which don't qualify for fast bitmap
+ * processing (different chip, not in hardware order)
+ */
+ if (array_info && (chip != array_info->chip ||
+ gpio_chip_hwgpio(desc) != descs->ndescs)) {
+ __clear_bit(descs->ndescs, array_info->get_mask);
+ __clear_bit(descs->ndescs, array_info->set_mask);
+ } else if (array_info) {
+ /* Exclude open drain or open source from fast output */
+ if (gpiochip_line_is_open_drain(chip, descs->ndescs) ||
+ gpiochip_line_is_open_source(chip, descs->ndescs))
+ __clear_bit(descs->ndescs,
+ array_info->set_mask);
+ /* Identify 'fast' pins which require invertion */
+ if (gpiod_is_active_low(desc))
+ __set_bit(descs->ndescs,
+ array_info->invert_mask);
+ }
+
descs->ndescs++;
}
+ if (array_info)
+ dev_dbg(dev,
+ "GPIO array info: chip=%s, size=%d, get_mask=%lx, set_mask=%lx, invert_mask=%lx\n",
+ array_info->chip->label, array_info->size,
+ *array_info->get_mask, *array_info->set_mask,
+ *array_info->invert_mask);
return descs;
}
EXPORT_SYMBOL_GPL(gpiod_get_array);
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 11e83d2eef89..b60905d558b1 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -183,6 +183,15 @@ static inline bool acpi_can_fallback_to_crs(struct acpi_device *adev,
}
#endif

+struct gpio_array {
+ struct gpio_desc **desc;
+ unsigned int size;
+ struct gpio_chip *chip;
+ unsigned long *get_mask;
+ unsigned long *set_mask;
+ unsigned long invert_mask[];
+};
+
struct gpio_desc *gpiochip_get_desc(struct gpio_chip *chip, u16 hwnum);
int gpiod_get_array_value_complex(bool raw, bool can_sleep,
unsigned int array_size,
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index 1b21dc7b0fad..8dede3e886af 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -17,11 +17,20 @@ struct device;
*/
struct gpio_desc;

+/**
+ * Opaque descriptor for a structure of GPIO array attributes. This structure
+ * is attached to struct gpiod_descs obtained from gpiod_get_array() and can be
+ * passed back to get/set array functions in order to activate fast processing
+ * path if applicable.
+ */
+struct gpio_array;
+
/**
* Struct containing an array of descriptors that can be obtained using
* gpiod_get_array().
*/
struct gpio_descs {
+ struct gpio_array *info;
unsigned int ndescs;
struct gpio_desc *desc[];
};
--
2.16.4