I'm trying to control (on/off) a voltage regulator that is mapped to a GPIO pin and powers an external device.
The device tree for the regulator has the following entry:
reg_usb1_vbus: usb1_vbus {
compatible = "regulator-fixed";
regulator-name = "usb1_vbus";
regulator-min-microvolt = <5000000>;
regulator-max-microvolt = <5000000>;
gpio = <&gpio3 28 0>;
enable-active-high;
};
As I read the documentation i got confused for it states:
Optional properties:
gpio: gpio to use for enable control
However, I can't export the sysfs interface of that GPIO and use it to control the power supply (just on/off) for the external device. In addition if I comment out the gpio = <&gpio3 28 0>; from the device tree, the external device gets no power (when it isn't commented the device is always powered).
The regulator has a sysfs interface exported:
80090000.usb-vbus power suspend_standby_state
device state type
microvolts subsystem uevent
name suspend_disk_state
num_users suspend_mem_state
however I can't write to any of the files.
What is the correct way to interpret the gpio: entry?
gpio to use for enable control
In which case I'm missing a mapping between a pin on which I want to have the regulator voltage.
gpio which will have the voltage from the regulator to power some external unit
In which case I'm missing a way to turn it on and off
I'm trying to control (on/off) a voltage regulator that is mapped to a GPIO pin and powers an external device.
...
What is the correct way to interpret the gpio: entry?
Seems like you're asking an XY question.
First the Y part regarding the GPIO.
The gpio DT entry you refer to would be for an enable/disable control by the regulator framework. It is intended for exclusive use by the regulator driver to control the (external?) regulator hardware. It is not intended for software control of the regulator outside the framework by the user (as you are trying to do).
This GPIO is defined as an output in drivers/regulator/core.c:
static int regulator_ena_gpio_request(struct regulator_dev *rdev,
const struct regulator_config *config)
{
...
ret = gpio_request_one(config->ena_gpio,
GPIOF_DIR_OUT | config->ena_gpio_flags,
rdev_get_name(rdev));
...
}
The GPIO pin is not read for "enable control", but has its value set in
regulator_ena_gpio_ctrl() in order to actively enable or disable the (external) regulator.
The inablity to export the same GPIO pin using sysfs when that pin is also declared in the Device Tree is easily explained. Once the driver acquires the specified GPIO for its use (through the DT), it is no longer unused, and you cannot export that GPIO through sysfs anymore.
GPIOs are a managed resource, and need to be allocated and freed (by a driver or sysfs) just like any other resource such as memory. If you were able to export this GPIO that was also used by the driver, then you would be able to put the GPIO into a state that was inconsistent with what the driver was doing. That in turn would lead to an unstable or misbehaving code.
In which case I'm missing a mapping between a pin on which I want to have the regulator voltage.
The GPIO pin specified in the Device Tree is a logic (i.e. digital) output. It is not the regulator output, which would be an analog output.
You should consult the schematic for your board to confirm that this GPIO is connected to a control input of a regulator.
As to the X part regarding enabling/disabling the regulator:
Software control of the regulator's output is documented in Documentation/power/regulator/consumer.txt
A consumer driver can get access to its supply regulator by calling :-
regulator = regulator_get(dev, "Vcc");
A consumer can enable its power supply by calling:-
int regulator_enable(regulator);
A consumer can disable its supply when no longer needed by calling :-
int regulator_disable(regulator);
The 'consumer" is an electronic device that is supplied power by a regulator.
Apparently the intended framework is have the "consumer driver" own and control its regulator, and not allow an external interface (e.g. sysfs) to interfere with this "consumer driver". If you insist on having userland control, then you could implement an ioctl() or sysfs interface to the "consumer driver" (to avoid conflict/contention with the regulator driver).
In which case I'm missing a way to turn it on and off
What you're really looking for seems to be (upper-layer) power management, and that has its own framework, of which regulators is a lower layer (which is normally not accessible for user control). You should study Documentation/driver-api/pm/devices.txt.
I am not extremely familiar with the regulator core in the kernel, but it seems to me that the regulator interface needs to give you access to the GPIO in a different way than the standad export GPIO method.
I have not looked into this, but it is possible the the regulator interface opens up a character device to userspace for control over the regulator. (Don't hold me to that)
I do see in the documentation and in the driver source code drivers/regulator/fixed.c that the GPIO is not a required DT attribute. You might be able to leave it out of the DT in which case the Driver will never acquire your GPIO, then you can manually control it through the standard export GPIO interface.
Related
I have a board, SoC running Linux 5+, with a electrical relay. The relay is triggered by a GPIO. I am looking for a good way to define a relay in a device tree file.
I define LEDs as
led {
compatible = "gpio-leds";
debug {
label = "debug";
gpios = ...
default-state = "off";
};
};
This results in
# ls /sys/class/leds/
debug
I would like to have the relay be something similar such as
# ls /sys/class/{relays,outputs,gpios}/
relay1
What is a good way to achieve this?
Since relay behaves as simply as GPIO output (or more precisely GPO), what you need is just name the corresponding line. It can be done by assigning gpio-line-names property of the GPIO controller in the ACPI or Device Tree. With a use of libgpiod tools (such as gpiofind, gpioinfo), that access GPIO controller via character device node, you may find your line and do the operations on it. Note, GPIO sysfs interface is deprecated and it will be removed from the kernel on a horizon of ~5 years or so.
I have two device tree nodes, one sets a gpio pin and the other one configures one i2c bus, ex:
&gpio2 {
en-gpio {
gpio-hog;
gpios = <5 0>;
output-high;
};
};
&i2c1 {
gpiom1: gpio#27 {
compatible = "microchip,mcp23008";
gpio-controller;
#gpio-cells = <2>;
reg = <0x27>;
};
};
How can i add a dependency between the i2c node and gpio one?
What i want to achieve is that the gpio pin should be set before the devices on i2c are initialized.
Short answer
You can't provide dependency between nodes in this case. But most likely the correct order is already taken care of in your case, and GPIO pin will be set before I2C device initialization, thanks to earlier initcall used for GPIO controller driver, and because gpio-hog is used. If you want to check it for your platform to be sure -- below are details.
Nodes relationship
As stated in Device trees II: The harder parts LWN article:
Naturally, in each case the device which provides the interrupt or GPIO will need to be initialized before it can be found and used. It wasn't very many kernel versions ago that this was a real problem. However in the 3.4 kernel, drivers gained the ability for their initialization (or probe) routine to return the error EPROBE_DEFER which would cause the initialization to be tried again later. So if a driver finds that a GPIO line is listed in the devicetree, but no driver has registered GPIOs for the target node yet, it can fail with EPROBE_DEFER and know it can try again later. This can even be used to remove the need for callbacks and delayed registration in board files, but it is really essential for devicetree, and happily it works quite well.
Alas, in your case it's probably not possible to specify dependency between nodes, so that your i2c1 or gpiom1 depends on gpio2. At least I don't see any gpios properties for I2C controllers or GPIO controllers in Documentation/devicetree/bindings/, that can be used for referencing your en-gpio. So it seems like you should rely on drivers loading order.
Driver dependencies
There are two possible dependencies between drivers:
If drivers are built-in (inside of kernel image): drivers can be initialized at different initcalls, thus being loaded in correct order
If drivers are loadable (.ko files): drivers can have dependencies, defined in kernel build system
As you didn't mention your platform, let's see how it works using BeagleBone Black board for example. You can use this as a template to find out how it's done on your platform.
Static dependencies
Let's check drivers init order:
From am33xx-l4.dtsi file we can see that:
GPIO controller: compatible = "ti,omap4-gpio"
I2C controller: compatible = "ti,omap4-i2c"
I2C device: compatible = "microchip,mcp23008"
Corresponding drivers for those compatible strings are:
GPIO controller: drivers/gpio/gpio-omap.c
I2C controller: drivers/i2c/busses/i2c-omap.c
I2C device: drivers/pinctrl/pinctrl-mcp23s08.c
Those drivers are initialized on next initcalls:
GPIO controller: postcore_initcall (=2)
I2C controller: subsys_initcall (=4)
I2C device: subsys_initcall (=4)
So GPIO controller driver will be initialized before I2C drivers.
Dynamic dependencies
What about dynamic dependencies? From corresponding Makefile and Kconfig files we can see config options and dependencies:
GPIO controller: CONFIG_GPIO_OMAP, tristate, doesn't depend on I2C stuff
I2C controller: CONFIG_I2C_OMA, tristate, doesn't depend on GPIO stuff
I2C device: CONFIG_PINCTRL_MCP23S08, tristate, depends on I2C
So if drivers are loaded in user-space as .ko files, it all depends on the order of their loading, user must take care of it in rootfs. Usually GPIO and I2C controller drivers are built-in, so no need to discuss this further, but just FYI, here is how the order is defined for modprobe tool.
Kernel Configuration
To check how drivers are built (built-in or loadable), one can check .config file. E.g. if multi_v7_defconfig is used:
CONFIG_GPIO_OMAP=y
CONFIG_I2C_OMAP=y
In that case both drivers are built-in, and we know that GPIO driver has earlier initcall than I2C one.
GPIO hogging
You did the right thing by declaring your pin as gpio-hog. You probably already know what it means, but I'll reference the explanation here for everyone else who is interested. From Documentation/devicetree/bindings/gpio/gpio.txt:
The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
providing automatic GPIO request and configuration as part of the
gpio-controller's driver probe function.
So this is as early as you can get. And if your GPIO controller driver is built-in and has initcall number smaller than one for I2C drivers, you can argue that your en-gpio pin will be set before I2C device driver init.
I have a MicroZed board with Xillinux 1.3 running on it. I wanted to interface an external SPI ADC to it, and write an application in linux to read values from the ADC. Zynq device's hardware SPI interface isn't enabled in Xillinux. How can I go about enabling it, I would have to recompile the FSBL and U-boot, but I don't know where to start. Can I just modify the Xillinux's Vivado design and proceed from there or will I have to start from scratch?
You should not have to modify FSBL or U-boot. You should only have to add the SPI controller to the device tree and update the programmable logic so that the SPI pins connect to your ADC.
Xilinx SDK has tools for creating the device tree file, described on the Build Device Tree Blob page.
I usually edit .dts files by hand, but you still need to run dtc to convert them to binary format as described on that page.
For an example, here is a .dts fragment for a zynq-zc770-xm013.dts board enabling SPI connected to a flash chip:
&spi0 {
status = "okay";
num-cs = <4>;
is-decoded-cs = <0>;
eeprom: at25#0 {
at25,byte-len = <8192>;
at25,addr-mode = <2>;
at25,page-size = <32>;
compatible = "atmel,at25";
reg = <2>;
spi-max-frequency = <1000000>;
};
};
you have to do 2 steps.
1- modify the hardware descriptor file (.h) of your board in your kernel sources and add the spi device. First, take a look at the schematic of the board and the datasheet of the processo to make sure to use the right device with the right name
2- add spidev on your kernel config
now build and boot the kernel, if you check on /dev/ you should find spidev** something.
I have to handle (i.e. turn on and off) my LCD Power Pin kernel and userspace both side.
We have configured the gpio pin in Mux.h,da850.c and board-da850-evm.c properly.
The problem is that when we configure this pin in kernel then this pin is not access by /sys/class/gpio.
We have configured this in in board-da850-evm.c as below,
ret = gpio_request(DA850_LCD_GP3, "LCD GP3");
if (ret)
pr_warning("Cannot open GPIO %d\n", DA850_LCD_GP3);
gpio_direction_output(DA850_LCD_GP3, 1);
gpio_set_value(DA850_LCD_GP3,1);
If we comment this section.and export from userspace then we used this pin form userspace successfully.
Is it possible to handle gpio form kernel and userspace?
Or do we need to write the gpio drive ?
I have developed a SPI platform driver for a single SPI device.Which SPI device we are using,that configuration can be given in Device Tree.probe() function of SPI platform driver is called when name matching happens with name give in driver and the same present in DT.
In SPI platform driver module_init() method, we register SPI device structure (struct spi_driver spidev_spi_driver) with function call: spi_register_driver().
Please refer to the (static struct spi_driver spidev_spi_driver) in below link for example.
Link: http://lxr.free-electrons.com/source/drivers/spi/spidev.c#L664
Here Probe() is one important method registered in this call.
When probe function is called, kernel passes pointer of SPI device (e.g struct spi_device *spi) in probe() function which is further utilized in read and write operation with SPI device.
All the above procedure happens only once for a single SPI device.
Now I have query here that if I want to use more than one SPI device present in my micro controller e.g. imx6 then how I will handle this situation?
How will I receive SPI device pointers in this case?
Is the probe function will be called twice (bcoz here only I get SPI device pointers from kernel)?
Do I need to create entries such as done in spidev_dt_ids:
http://lxr.free-electrons.com/source/drivers/spi/spidev.c#L657
I haven't worked on specifically spi device, but I think I might give you some basic idea. The logic is that probe is called whenever there is matching between device->name and device_driver->name. So 2 devices can use same driver but 2 drivers should not be there for same device.
For configuring 2 devices to same driver, the 2 device will be registered on same name and hence same probe will be called. But then in probe you can differentiate. You will have access to the device struct of spi which you can use to set one parameter to distinguish and set the relevant parameters.
One more approach is like using core framework used by i2c in which general functionality functions are made and used by client driver whenever needed.
I hope this helps.