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gpiolib: allow simultaneous setting of multiple GPIO outputs

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Introduce new functions gpiod_set_array & gpiod_set_raw_array to the consumer
interface which allow setting multiple outputs with just one function call.
Also add an optional set_multiple function to the driver interface. Without an
implementation of that function in the chip driver outputs are set
sequentially.

Implementing the set_multiple function in a chip driver allows for:
- Improved performance for certain use cases. The original motivation for this
  was the task of configuring an FPGA. In that specific case, where 9 GPIO
  lines have to be set many times, configuration time goes down from 48 s to
  20 s when using the new function.
- Simultaneous glitch-free setting of multiple pins on any kind of parallel
  bus attached to GPIOs provided they all reside on the same chip and bank.

Limitations:
  Performance is only improved for normal high-low outputs. Open drain and
  open source outputs are always set separately from each other. Those kinds
  of outputs could probably be accelerated in a similar way if we could
  forgo the error checking when setting GPIO directions.

Change log:
  v6: - rebase on current linux-gpio devel branch
  v5: - check can_sleep property per chip
      - remove superfluous checks
      - supplement documentation
  v4: - add gpiod_set_array function for setting logical values
      - change interface of the set_multiple driver function to use
        unsigned long as type for the bit fields
      - use generic bitops (which also use unsigned long for bit fields)
      - do not use ARCH_NR_GPIOS any more
  v3: - add documentation
      - change commit message
  v2: - use descriptor interface
      - allow arbitrary groups of GPIOs spanning multiple chips

Signed-off-by: Rojhalat Ibrahim <[email protected]>
Reviewed-by: Alexandre Courbot <[email protected]>
Reviewed-by: Mark Brown <[email protected]>
Signed-off-by: Linus Walleij <[email protected]>
This commit is contained in:
Rojhalat Ibrahim 2014-11-04 17:12:06 +01:00 • committed by Linus Walleij
commit 5f42424354
4 changed files with 237 additions and 0 deletions
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27
Documentation/gpio/consumer.txt
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@ -199,6 +199,33 @@ The active-low state of a GPIO can also be queried using the following call:
Note that these functions should only be used with great moderation ; a driver
should not have to care about the physical line level.
Set multiple GPIO outputs with a single function call
-----------------------------------------------------
The following functions set the output values of an array of GPIOs:
void gpiod_set_array(unsigned int array_size,
struct gpio_desc **desc_array,
int *value_array)
void gpiod_set_raw_array(unsigned int array_size,
struct gpio_desc **desc_array,
int *value_array)
void gpiod_set_array_cansleep(unsigned int array_size,
struct gpio_desc **desc_array,
int *value_array)
void gpiod_set_raw_array_cansleep(unsigned int array_size,
struct gpio_desc **desc_array,
int *value_array)
The array can be an arbitrary set of GPIOs. The functions will try to set
GPIOs belonging to the same bank or chip simultaneously if supported by the
corresponding chip driver. In that case a significantly improved performance
can be expected. If simultaneous setting is not possible the GPIOs will be set
sequentially.
Note that for optimal performance GPIOs belonging to the same chip should be
contiguous within the array of descriptors.
GPIOs mapped to IRQs
--------------------
GPIO lines can quite often be used as IRQs. You can get the IRQ number