I have a question about irq in linux kernel.
I enable a irq using request_threaded_irq(..). But sometimes we need to disable irq using disable_irq().
Depending on the situation, it may be necessary to enable it again.
Can I check a specific irq is already enabled before enable irq? To prevent enable again.
Is there any api to check a specific irq is enabled or disabled?
Thank you
Related
In reference to the QEMU x86_64 machine option kernel_irqchip=on|off, the description reads:
Controls in-kernel irqchip support for the chosen accelerator when available
What is an "irqchip"?
An "irqchip" is KVM's name for what is more usually called an "interrupt controller". This is a piece of hardware which takes lots of interrupt signals (from devices like a USB controller, disk controller, PCI cards, serial port, etc) and presents them to the CPU in a way that lets the CPU control which interrupts are enabled, be notified when a new interrupt arrives, dismiss a handled interrupt, and so on.
An emulated system (VM) needs an emulated interrupt controller, in the same way that real hardware has a real hardware interrupt controller. In a KVM VM, it is possible to have this emulated device be in userspace (ie QEMU) like all the other emulated devices. But because the interrupt controller is so closely involved with the handling of simulated interrupts, having to go back and forth between the kernel and userspace frequently as the guest manipulates the interrupt controller is bad for performance. So KVM provides an emulation of an interrupt controller in the kernel (the "in-kernel irqchip") which QEMU can use instead of providing its own version in userspace. (On at least some architectures the in-kernel irqchip is also able to use hardware assists for virtualization of interrupt handling which the userspace version cannot, which further improves VM performance.)
The default QEMU setting is to use the in-kernel irqchip, and this gives the best performance. So you don't need to do anything with this command line option unless you know you have a specific reason why the in-kernel irqchip will not work for you.
I use and build a kernel 4.14 which is already running on a ARM processor.
Now I would include the MCP23S08 driver (pinctrl-mcp23s08.c)
For that, I use make menuconfig to enable the driver. Unfortunately, I could not find an entry for the Pin Control subsystem in which the driver should be.
For testing, I checked out the kernel 4.17 in which the entry Device Driver->Pin Controlls exist. According to the entry in LKDD I think something changed in the configuration method between kernel 4.14 and 4.15.
Does someone now, how to activate the Pin Control subsystem in kernel 4.14? Thank you for any hint!
Ok, I found a way to enable the Pin control subsystem:
At least in that kernel version (4.14) the pin control subsystem is a machine configuration. I activated it in the /arch/arm/mach-*/Kconfig file. After that, the entry was shown in the kernel menuconfig.
Linux kernel 2.6
I've got an fpga that is loaded over GPIO connected to a development board running linux.
The fpga will transmit and receive data over the pci-express bus. However, this is enumerated
at boot and as such, no link is discovered (because the fpga is not loaded at boot).
How can I force re-enumeration of the pci-e bus in linux?
Is there a simple command or will I have to make kernel changes?
I need the capability to hotplug pcie devices.
As root, try the following command:
echo "1" > /sys/bus/pci/rescan
See this link for more information: http://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-pci
I wonder what platform you are on: A work around (aka hack) for this that works on x86 systems is to have the BIOS basically statically configure a PCI device at whatever bus, device, function the FPGA normally lands on, then the OS will enumerate the device and reserve the PCI space for it (even though the device isn't really there). Then in your device driver you will have to do some extra things like setup the BARs and int lines manually after the fpga has been programmed. Of course this requires modifying the BIOS, which if you are working with a BIOS vendor you can contract them to make this change for you, if you are not working with a BIOS vendor then it will be much harder... Also keep in mind that I was working on VxWorks on x86, and we had a AMI make a custom BIOS for our boards...
If you don't have a BIOS, then consider programming it in the bootloader, there you already have the ability to read from disk, and adding GPIO capabilities probably isn't too difficult (assuming you are using jtag and GPIOs?), in fact depending on what bootloader you use it might already be able to do GPIO?
The issues with modifying the kernel to do this is that you have to find the sweet spot where you can read the bitfile, before the PCI enumeration... If for example the disk device drivers are initialized after PCI, then obviously you must do some radical changes to the kernel just to read the bitfile prior to PCI enumeration, which might cause other annoying problems...
One other option which you may have already discovered, and which is really only ok for development time: Power up the system, program the fpga board, then do a reset (without power cycle, for example: sudo reboot now), the FPGA should keep its configuration, and linux should enumerate it...
After turning on your computer, the BIOS enumerates the PCI bus and attempts to fulfill all IO space and memory mapped IO (MMIO) requests. It sets up these BAR's initially, and when the operating system loads these BAR's can be changed by the OS as it sees fit while the PCI bus driver enumerates the bus yet again. It is even possible for the superuser of the system to run the command setpci to change these BAR's after the BIOS has already attempted to configure them and the OS has loaded (may cause drivers to fail and several other bad things if done improperly).
I have had to do this in cases where the card in question was not assigned any resources by the BIOS since the region requested required a 64-bit address and the BIOS only operated with 32-bit address assignments. I was able to go in after-the-fact and change these addresses (originally assigned by the BIOS) to whatever addresses I saw fit, insert the kernel module, and my driver would map and use these newly-assigned addresses for the card without knowing the difference.
The problem that exists with hotplugging PCI-Express cards is that the power to the slot, itself, cannot be turned on/off without specific hotplug controllers that need to exist on the motherboard/backplane. Not having these hotplug controllers to turn the slot's power off may lead to shorts between the tiny pins when the card is physically inserted and/or removed if power is still present. Hotplug events, however, can be initiated by either end (the host or the endpoint device). This does not seem to be the case, however if your FPGA already has a link established with the root complex, a possible solution to your problem would be to generate hotplug interrupts to cause a bus rescan in the OS.
There is a major problem, though -- if your card does not actually obtain a link to the root complex, it won't be able to generate any hotplug events; which seems to be the case. After booting, the FPGA should toggle the PRESENT line on the PCIe bus to tell the OS there is a card ready to be enumerated. Once detected, the OS should attempt to establish a link to the card and assign memory regions to the device. After the OS enumerates the card you'll be able to load drivers against it and see it in lspci. You stated you're using kernel 2.6, which does have support for hotplugging and dynamic resource allocation so this method should work as long as your FPGA supports the ability to toggle the PRESENT PCIe line, too.
I tried to enable watchdog through IPMI on FreeBSD 7.
According to IPMI spec v2.0. It's able to set NMI interrupt by set pre-timeout action bit.
The timeout action returns correct, but there is no response with NMI interrupt.
I wander whether it need other configuration somewhere else.
Any suggestions?
Thanks.
FreeBSD watchdogd daemon is what you want. It initialises correspondent device (ichwd or amdsbwd - it should show up in your dmesg if you had enabled it) or uses software watchdog.
I'm looking for either a kernel mode call that I can make from a driver, a userland utility, or a system call that will ask the Kernel to look at the PCI bus and either completely re-run its initialization, or initialize a specific device. Specifically, I need the Kernel to recognize a device that was added to the bus after boot and then configure its address space, interrupt, and other configuration parameters, and finally enable the device so that I can load the driver for it (unless this all happens as part of the driver load).
I'm stuck on the 2.4.x series Kernel for this, and am currently working with 2.4.20, but will be moving to 2.4.37 if it matters. The distro is a stripped down Red Hat 7.3 running in a ram disk, but I can add in whatever tools are needed to get this working (as long as they play nice with 2.4 series).
If some background would help clarify what I'm trying to do: From a cold boot, once in Linux I use GPIO to program an FPGA. Part of the FPGA, once programmed, implements a simple PCI device. Currently, after programming the FPGA, I reboot the system and Linux recognizes the device after coming up and loads the driver for it.
Instead of needing that reboot, I'd like to simply ask the Kernel to do whatever it does during boot up to find PCI devices (I have the Kernel configured to find PCI devices on its own, instead of asking the BIOS for that information, so the BIOS won't need to know about this device (I hope)).
I believe that Linux is capable of seeing the device after it is programmed but before a reboot, because scanpci will show the device after I program it, as will lspci -H 1. I just need a way to get it into /proc/pci, configured and enabled.
This below command will help the user to rescan it complete root hub.
echo "1" > /sys/class/pci_bus/0000\:00/rescan
You could speed up the reboot with kexec, if you don't figure out how to get the PCI scan redone. You could ask this on the LKML, if you haven't already.
unloading/reloading the module doesn't help, does it?
http://www.linuxjournal.com/article/5633 suggests you should be able to do it with 2.4 kernels using pcihpfs.
If that isn't working, maybe the driver doesn't support hotplug?
It would probably crash the system if you reconfigured the addresses of other PCI devices while they are in use.
A better way would be to just configure the new card. If your kernel has support for Cardus devices, it already knows how to configure a newly-inserted PCI device (which is what Cardbus is). You just need to figure out how to get the kernel to do it...
It should be possible for a kernel module to do this. Even if you can't get built-in hotplug code, you should be able to set the pci resources using calls to pci_bus_write_config_dword() and friends. There is probably some IRQ routing setup to do as well.