I have a little driver that is handling a gpio that when enabled should tell the system to sleep/wake when a button is pressed. If its held down it should power off.
On WinCE there is a very easy to use mechanism (SetSystemPowerState) but there doesn't appear to be something similar on linux.
We also don't have dbus...
update:
I may have found the answer
Shutdown (embedded) linux from kernel-space
Though it doesn't really say how to sleep but i think I'll be able to figure the rest out. This doesn't seem like the proper way to handle a linux kernel driver since the module is built into the kernel. It doesn't appear that I have all the power states available to switch to without adding packages outside of the kernel.
If you want to suspend your system entirely, you can use /sys/power/state interface like belows.
echo "mem" > /sys/power/state
It calls state_store() function in kernel/power/main.c to suspend your system into memory. Instead of "mem", you can use "standby" or "disk" only if your system supports them.
The most general way would be to initiate the process from kernelspace as a userspace helper:
static const char * const set_power_argv[] =
{ "/bin/echo", "mem", "/sys/power/state", NULL };
call_usermodehelper(shutdown_argv[0], shutdown_argv, NULL, UMH_NO_WAIT);
However, location of echo command and power driver can differ in your system.
Related
I have a general question about linux device driver. More often I get confused which actions are allowed or not allowed to perform in a linux device driver?
Is there any rules or kind of lookup list to follow?
for instance with the following examples, which are not allowable?
msleep(1000);
al = kmallock(sizeof(val));
printk(KERN_ALERT "faild to print\n";
ret = adc_get_val()*0.001;
In linux device driver programming it depends in which context you are. There are two contexts that need to be distinguished:
process context
IRQ context.
Sleeping can only be done while in process context or you schedule the work for later execution (there are several mechanism available to do that). This is a complex topic that cannot be described in a paragraph.
Allocating memory can sleep, it depends with which parameters/flags kmalloc is invoked.
print can always be called (once the kernel has been invoked), otherwise use early_printk.
I don't know what the function add_get_val does. It is not part of the linux kernel. And as has already been commented, float values cannot be easily used in the kernel.
I'm trying to enable polling support for a serial over USB driver on an android kernel, so that I can debug it using kgdboc. I based myself on the code from these githubs:
https://github.com/dankex/kgdb-android
https://github.com/jacktang310/KernelDebugOnNexus6P
However, I can't find a way to enable and use char by char polling mode via a C program on userland. Which makes debugging very difficult, since the only thing I can do is to set kgdboc to /dev/ttyGS0 and then send "g" to sysrq-trigger, and pray it works.
In other terms, I need a userland program that triggers the code path which reaches the following operations on the tty_operations structure:
.poll_init = gs_poll_init,
.poll_get_char = gs_poll_get_char,
.poll_put_char = gs_poll_put_char,
Instead, whenever I write to /dev/ttyGS0 I trigger the "write" operation.
Any help will be greatly appreciated.
Thanks!
I ended up creating a driver that exports a sysfs node as Chris Stratton suggested.
I based myself on this tutorial
Coming form this question yesterday, I decided to port this library to my board. I was aware that I needed to change something, so I compiled the library, call it on a small program and see what happens. The 1st problem is here:
// Check for GPIO and peripheral addresses from device tree.
// Adapted from code in the RPi.GPIO library at:
// http://sourceforge.net/p/raspberry-gpio-python/
FILE *fp = fopen("/proc/device-tree/soc/ranges", "rb");
if (fp == NULL) {
return MMIO_ERROR_OFFSET;
}
This lib is aimed for Rpi, os the structure of the system on my board is not the same. So I was wondering if somebody could tell me where I could find this file or how it looks like so I can find it by my self in order to proceed the job.
Thanks.
You don't necessarily want that "file" (or more precisely /proc node).
The code this is found in is setting up to do direct memory mapped I/O using what appears to be a pi-specific gpio-flavored version of the /dev/mem type of device driver for exposing hardware special function registers to userspace.
To port this to your board, you would need to first determine if there is a /dev/mem or similar capability in your kernel which you can activate. Then you would need to determine the appropriate I/O registers for GPIO pins. The pi-specific code is reading the Device Tree to figure this out, but there are other ways, for example you can manually read the programmer's manual of the SoC on which you are running.
Another approach you can consider is adding some small microcontroller (or yes, barebones ***duino) to the system, and using that to collect information from various sensors and peripherals. This can then be forwarded to the SoC over a UART link, or queried out via I2C or similar - add a small amount of cost and some degree of bottleneck, but also means that the software on the SoC then becomes very portable - to a different comparable chip, or perhaps even to run on a desktop PC during development.
Is it possible to pin a softirq, or any other bottom half to a processor. I have a doubt that this could be done from within a softirq code.
But then inside a driver is it possible to pin a particular IRQ to a
core.
From user mode, you can easily do this by writing to /proc/irq/N/smp_affinity to control which processor(s) an interrupt is directed to. The symbols for the code implementing this are not exported though, so it's difficult to do from the kernel (at least for a loadable module which is how most drivers are structured).
The fact that the implementing function symbols aren't exported is a sign that the kernel developers don't want to encourage this. Presumably that's because it takes control away from the user. And also embeds assumptions about number of processors and so forth into the driver.
So, to answer your question, yes, it's possible, but it's discouraged, and you would need to do one of several "ugly" things to implement it ((a) change kernel exports, (b) link your driver statically into main kernel, or (c) open/write to the proc file from kernel mode).
The usual way to achieve this is by writing a user-mode program (can even be a shell script) that programs core numbers/masks into the appropriate proc file. See Documentation/IRQ-affinity.txt in the kernel source directory for details.
I would like to disable c-states on my computer.
I disabled c-state on BIOS but I don't obtain any result. However, I found an explanation :
"Most newer Linux distributions, on systems with Intel processors, use the “intel_idle” driver (probably compiled into your kernel and not a separate module) to use C-states. This driver uses knowledge of the various CPUs to control C-states without input from system firmware (BIOS). This driver will mostly ignore any other BIOS setting and kernel parameters"
I found two solutions to solve this problem but I don't know how to apply:
1) " so if you want control over C-states, you should use kernel parameter “intel_idle.max_cstate=0” to disable this driver."
I don't know neither how I can check the value (of intel_idle.max_cstate ) and neither how I can change its value.
2) "To dynamically control C-states, open the file /dev/cpu_dma_latency and write the maximum allowable latency to it. This will prevent C-states with transition latencies higher than the specified value from being used, as long as the file /dev/cpu_dma_latency is kept open. Writing a maximum allowable latency of 0 will keep the processors in C0"
I can't read the file cpu_dma_latency.
Thanks for your help.
Computer:
Intel Xeon CPU E5-2620
Gnome 2.28.2
Linux 2.6.32-358
To alter the value at boot time, you can modify the GRUB configuration or edit it on the fly -- the method to modify that varies by distribution. This is the Ubuntu documentation to change kernel parameters either for a single boot, or permanently. For a RHEL-derived distribution, I don't see docs that are quite as clear, but you directly modify /boot/grub/grub.conf to include the parameter on the "kernel" lines for each bootable stanza.
For the second part of the question, many device files are read-only or write-only. You could use a small perl script like this (untested and not very clean, but should work) to keep the file open:
#!/usr/bin/perl
use FileHandle;
my $fd = open (">/dev/cpu_dma_latency");
print $fd "0";
print "Press CTRL-C to end.\n";
while (1) {
sleep 5;
}
Redhat has a C snippet in a KB article here as well and more description of the parameter.