I find the driver specific stuff in /sys/class/graphic/XM_403
But in /dev/ is no XM_403 file.
Here is the pertinent code.
graphic_class = class_create(THIS_MODULE,"graphic");
device_create(graphic_class,NULL,MKDEV(MAJOR_NR,minor),NULL,"XM_403");
device_create creates a file within the sysfs, exactly what you are seeing.
Usually it's udev that creates the device file.
Related
I am pretty new to linux kernel.I am trying to generate PWM through linux. The API man talks about a sysfs interface. I want to implement a userspace program in C. But using PWM forces me to use a command line. Furthermore, using read, write is a problem in C as when I am using cd, it is changing path directory.
Thus the path is variable. Is there any way I can pass values to pwm_config() without using sysfs? Perhaps through ioctl? If yes, then what would be the procedure?
Application C code:
void main(){
int export = open("/sys/class/pwm/pmwchip0/export",O_WRONLY);
int period,duty_cycle,enable;
if(export == -1)
{
perror("Export:");
}
and so on for other files like period and duty cycle.
When I try to run my application I get the following error.
Export:: No such file or directory
Export_write: Bad file descriptor
Period_write:: Bad file descriptor
Duty_cycle_write:: Bad file descriptor
Enable_write:: Bad file descriptor
As far as I know, the sysfs is the only standard userspace interface to PWM. But anything you can do from the command line can be done in C (the shell is written in C, after all).
The problem you are having with cd is not actually a problem. Inside sysfs the directories in /sys/class/pwd/* are actually symbolic links to the proper devices. In your case /sys/class/pwm/pwmchip0 is a symlink to /sys/devices/soc0/amba/f8001000.timer/pwm/pwmchip0.
The funny thing is that some shells, when you cd a symbolic link will resolve to the real directory, but other shells will actually keep the symlink name as the current directory.
But that issue with the directory symlinks should not be an issue for you. A C program willing to manage PWM devices should not change the working directory. Instead open the files with the full path:
open("/sys/class/pwm/pwmchip0/npwm", O_RDONLY);
and so on.
So I have compiled the driver for my USB wireless adapter.
Now I need to know where I should copy the .ko file to. The question is really the following:
What is the difference between
/lib/modules/(uname -r)/build
and
/lib/module/(uname -r)/kernel/drivers
?
Thank you already
When I add the .ko file to
/lib/module/(uname -r)/kernel/drivers/net/wireless/
the driver will be used to drive my USB adapter when I start the computer, at least when I execute 'depmod' after copying the file to a folder under .../kernel/drivers/net/wireless/ or .../kernel/net/wireless/
When I copy the driver to a folder under .../build the driver which is also a module isn't used to drive my USB adapter when I start the computer. Also when placed under build, 'modprobe' can't find the module after executing 'depmod'.
This actually tells me that .../build is never a good choice for placing a driver.
OK, so I have this embedded kernel whose network card used to work fine with the LLTEMAC option. The new one with LL_TEMAC doesn't. I still see the code with LLTEMAC in the source, but not in the available option in the .config file:
$ ack-grep LLTEMAC
drivers/net/ethernet/xilinx/xilinx_lltemac/Makefile:10:obj-$(CONFIG_XILINX_LLTEMAC) := xilinx_temac.o
drivers/net/ethernet/xilinx/xilinx_lltemac/xlltemac_main.c:2: * Xilinx Ethernet: Linux driver for the XPS_LLTEMAC core.
drivers/net/ethernet/xilinx/xilinx_lltemac/xlltemac_main.c:452:#ifdef CONFIG_XILINX_LLTEMAC_MARVELL_88E1111_RGMII
...
include/linux/xilinx_devices.h:83:/* LLTEMAC platform data */
Is there a way to compile the kernel with this removed option ?
Simply adding CONFIG_XILINX_LLTEMAC=y CONFIG_XILINX_LLTEMAC_MARVELL_88E1111_GMII=y to the .config file does not do anything as the dislaimer states: # Automatically generated file; DO NOT EDIT.
Thanks.
Why not just update this individual driver to understand the new configuration option?
I'm developing a device driver for embedded linux(ARM).
How can I compile the KO file generated as a part of the kernel,
in a way that the module will be loaded in boot ?
this is the first time I need to compile the driver into the kernel and not as a loadable module. so I'm not sure how to do it.
Thanks,
Ramon.
For your first question, I assume that you want to build your driver statically into the kernel image(not as a module). First, you select a directory in drivers directory where you want to put your driver files. Assume you want to put your files in drivers/char/. Copy your files into this directory. There will be a Kconfig file in the drivers/char/ directory, open it and add an entry like this in the before the endmenu.
config MYDRIVER
bool "This is a driver for something"
default n
help
This is a test driver.
Save the file and open Makefile in the same directory. Goto end of the file and add the following entry.
obj-$(CONFIG_MYDRIVER) += mydriver.o
That's it you have added the file to the kernel tree. Now, as usual, do make menuconfig and select MYDRIVER.
See this Kernel Compilation article for more info.
You need to build your device driver as a built-in. You can either edit your kernel .config file manually and change "=m" to "=y" for the CONFIG option that belongs to your module, or use make menuconfig to change <M> to <*> for your device driver.
before -> <M> Your Device Driver Name Here
after -> <*> Your Device Driver Name Here
Inotify won't trigger on file-changes in /sys - what ways are there to subscribe to changes in there?
Events that change /sys are usually handled by udev. So, you can add udevd rules to handle the events or use libudev to access and monitor the sysfs. I just found some tutorial here: http://www.signal11.us/oss/udev/
Use udev and udev rules to get a notification to changes (hardware hotplug, drivers load, firmware load etc.) that are reflected in /sys.
See http://hackaday.com/2009/09/18/how-to-write-udev-rules/ for details
To be notified on a change on a /sys file or directory, I use the polling objects from python.
import select
poll_objet = select.poll()
fd_object = file("/sys/what_you_want_to_survey", "r")
poll_objet.register(fd_object) # I use the select.POLLPRI | select.POLLERR combination in my code ;)
result = poll_object.poll()
where result is a list of (fd, event) that were touched.