On 8/3/22 11:59, Quentin Schulz wrote:
Hi Heinrich,
On 8/2/22 14:28, Heinrich Schuchardt wrote:
Provide a man-page for the gpio command.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
doc/usage/cmd/gpio.rst | 90 ++++++++++++++++++++++++++++++++++++++++++ doc/usage/index.rst | 1 + 2 files changed, 91 insertions(+) create mode 100644 doc/usage/cmd/gpio.rst
diff --git a/doc/usage/cmd/gpio.rst b/doc/usage/cmd/gpio.rst new file mode 100644 index 0000000000..f6a5668388 --- /dev/null +++ b/doc/usage/cmd/gpio.rst @@ -0,0 +1,90 @@ +.. SPDX-License-Identifier: GPL-2.0+:
+gpio command +============
+Synopsis +--------
+::
+ gpio <input|set|clear|toggle> <pin> + gpio read <name> <pin> + gpio status [-a] [<bank>|<pin>]
+The gpio command is used to access General Purpose Inputs/Outputs.
+gpio input +----------
+Switch the GPIO *pin* to input mode.
+gpio set +--------
+Switch the GPIO *pin* to output mode and set the signal to 1.
I think this is supposed to follow the GPIOD_ACTIVE_LOW/GPIOD_ACTIVE_HIGH flag. So I think it's better to say "set the state to active"? Maybe add a few words on this active high/low thing to explicit that using gpio set does not necessarily mean that the GPIO output will have some voltage.
There is no string GPIOD_ACTIVE_HIGH in U-Boot.
include/asm-generic/gpio.h:124: #define GPIOD_ACTIVE_LOW BIT(3) /* GPIO is active when value is low */
The gpio command lacks the capability to set active high or active low. It is not even displayed.
The function description of dm_gpio_get_value() documents the return value as 0 for inactive, 1 for active.
The function description of gpio_get_value() documents its return value as 0 for low or 1 for high.
The uclass implements gpio_get_value() by calling dm_gpio_get_value() without inverting the value.
One of both functions is incorrectly documented!
dm_gpio_get_value() calls _gpio_get_value() which calls the driver's get_value() function and inverts the value if GPIOD_ACTIVE_LOW is set.
The structure struct dm_gpio_ops lacks any documentation of the meaning of the return value.
To sum it up:
The function documentation is a mess and leaves it unclear what a value of 0 or 1 in the gpio command means.
The first thing to do is to get the documentation of struct dm_gpio_ops updated. Next ensure that all drivers implement it this way.
Once the yet to find maintainer of GPIO has done this we can revisit the documentation.
+gpio clear +----------
+Switch the GPIO *pin* to output mode and set the signal to 0.
Ditto.
+gpio toggle +-----------
+Switch the GPIO *pin* to output mode and reverse the signal state.
+gpio read +---------
+Read the signal state of the GPIO *pin* and save it in environment variable +*name*.
+gpio status +-----------
+Display the status of one or multiple GPIOs. By default only claimed GPIOs +are displayed.
+-a + Display GPIOs irrespective of being claimed.
+bank + Name of a bank of GPIOs to be displayed.
+pin + Name of a single GPIO to be displayed or manipulated.
+Examples +--------
+Switch the status of a GPIO::
+ => gpio set a5 + gpio: pin a5 (gpio 133) value is 1
and I guess we should maybe patch the gpio cmd to say here "high" instead of "1"?
For an active low GPIO value 1 might mean low.
It would be helpful to provide a way to display if a GPIO is active high or active low. But this patch is about documenting the existing functionality.
Best regards
Heinrich
+ => gpio clear a5 + gpio: pin a5 (gpio 133) value is 0
ditto
+ => gpio toggle a5 + gpio: pin a5 (gpio 133) value is 1
ditto
+ => gpio read myvar a5 + gpio: pin a5 (gpio 133) value is 1
ditto
+ => echo $myvar + 1 + => gpio toggle a5 + gpio: pin a5 (gpio 133) value is 0
ditto
+ => gpio read myvar a5 + gpio: pin a5 (gpio 133) value is 0
ditto
Cheers, Quentin