i started with device driver for arm ... there i saw for each handler mention --- __attribute__((interrupt( irq ))) -.I am confused how this attribute will place a call to our driver routine ..??
IRQ of arm have following Vector address--- 0x00000018 (or 0xFFFF0018)
As there can be many interrupt handler on same line. Suppose if we have 4 device driver each with its own IRQ to be reistered.
Means some startup code will be provided by the GCC compiler for the IRQ handler & compiler will place call to our routine in that startup code for interrupt handler ..... Am i right ...?
From GCC docs for interrupt attribute:
The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
You can use objdump easily to see how this attribute changes your binary which should clarify the situation for you much better.
The attribute should ONLY be used by interrupt handler of the OS and NOT by interrupt handler of a specific driver. The OS will read the IRQ vector/number and call the appropriate driver function to service the IRQ. You only need to register your driver/ISR with the OS.
Related
I'm looking through the source but I can't find where the low level asm interrupt_vector and fast_interrupt_vector code is or where the higher level C code called by low level vectors is. Where is the interrupt code for arm at?
The interrupt handlers are in the device driver code. Each device type has its own driver somewhere in the driver subdirectory. The driver initialization code typically requests an irq from the kernel, passing a function pointer to the handler as a parameter. This means that the service routines are not collected together, but are essentially "all over the place".
I have written a simple character driver and requested IRQ on a gpio pin and wrtten a handler for it.
err = request_irq( irq, irq_handler,IRQF_SHARED | IRQF_TRIGGER_RISING, INTERRUPT_DEVICE_NAME, raspi_gpio_devp);
static irqreturn_t irq_handler(int irq, void *arg);
now from theory i know that Upon interrupt the interrupt Controller with tell the processor to call do_IRQ() which will check the IDT and call my interrupt handler for this line.
how does the kernel know that the interrupt handler was for this particular device file
Also I know that Interrupt handlers do not run in any process context. But let say I am accessing any variable declared out side scope of handler, a static global flag = 0, In the handler I make flag = 1 indicating that an interrupt has occurred. That variable is in process context. So I am confused how this handler not in any process context modify a variable in process context.
Thanks
The kernel does not know that this particular interrupt is for a particular device.
The only thing it knows is that it must call irq_handler with raspi_gpio_devp as a parameter. (like this: irq_handler(irq, raspi_gpio_devp)).
If your irq line is shared, you should check if your device generated an IRQ or not. Code:
int irq_handler(int irq, void* dev_id) {
struct raspi_gpio_dev *raspi_gpio_devp = (struct raspi_gpio_dev *) dev_id;
if (!my_gpio_irq_occured(raspi_gpio_devp))
return IRQ_NONE;
/* do stuff here */
return IRQ_HANDLED;
}
The interrupt handler runs in interrupt context. But you can access static variables declared outside the scope of the interrupt.
Usually, what an interrupt handler does is:
check interrupt status
retrieve information from the hardware and store it somewhere (a buffer/fifo for example)
wake_up() a kernel process waiting for that information
If you want to be really confident with the do and don't of interrupt handling, the best thing to read about is what a process is for the kernel.
An excellent book dealing with this is Linux Kernel Developpement by Robert Love.
The kernel doesn't know which device the interrupt pertains to. It is possible for a single interrupt to be shared among multiple devices. Previously this was quite common. It is becoming less so due to improved interrupt support in interrupt controllers and introduction of message-signaled interrupts. Your driver must determine whether the interrupt was from your device (i.e. whether your device needs "service").
You can provide context to your interrupt handler via the "void *arg" provided. This should never be process-specific context, because a process might exit leaving pointers dangling (i.e. referencing memory which has been freed and/or possibly reallocated for other purposes).
A global variable is not "in process context". It is in every context -- or no context if you prefer. When you hear "not in process context", that means a few things: (1) you cannot block/sleep (because what process would you be putting to sleep?), (2) you cannot make any references to user-space virtual addresses (because what would those references be pointing to?), (3) you cannot make references to "current task" (since there isn't one or it's unknown).
Typically, a driver's interrupt handler pushes or pulls data into "driver global" data areas from which/to which the process context end of the driver can transfer data.
This is to reply your question :-
how does the kernel know that the interrupt handler was for this particular >device file?
Each System-On-Chip documents will mention interrupt numbers for different devices connected to different interrupt lines.
The Same Interrupt number has to be mentioned in the Device Tree entry for instantiation of device driver.
The Device driver's usual probe function parses the Device tree data structure and reads the IRQ number and registers the handler using the register_irq function.
If there are multiple devices to a single IRQ number/line, then the IRQ status register(for different devices if mapped under the same VM space) can be used inside the IRQ handler to differentiate.
Please read more in my blog
I am trying to write a Kernel Module that I can use to service PCIe MSI interrupts. Right now I am having trouble trying to configure my interrupts and am trying to follow along with "Linux Device Drivers Ed. 3" The book states:
"The driver doesn't need to bother checking the interrupt number, because the value found in PCI_INTERRUPT_LINE is guaranteed to be the right one."
So of course this seems to be the logical way to setup my interrupts:
err = pci_read_config_byte(dev, PCI_INTERRUPT_LINE, &myirq);
if(err)
{
printk(KERN_WARNING "Could not get IRQ number\n");
return err;
}
err = request_irq(myirq, fpga_isr, IRQF_SHARED, fpga_driver.name, dev);
Now this registers me for interrupt 60. I then go about using jTag to manually trigger an interrupt and I get a Kernel message saying that the interrupt does not have a handler attatched to it (interrupt 576). If I hardcode irq_line to 576 I then fail the request_irq.
What is the best way to find out my interrupt line? and why can I not get the IRQ that I need?
One more thing, during boot, my device is automatically set to IRQ pin 1 (Legacy interrupt A) which correseponds to irq line 572 which is also the value stored in dev->irq. If the boot sequence automatically set the IRQ to pin 0 (Legacy interrupts disabled) would dev->irq point to my MSI interrupt # 576?
For MSI, you need to enable the MSI interrupt on your device first with pci_enable_msi. The MSI interrupt is not the same as the "standard PCI" interrupt. After calling pci_enable_msi, the interrupt number should be gotten from pci_dev->irq for calling request_irq. Look for an example in the kernel source tree.
More info in Documentation/PCI/MSI-HOWTO.txt
can anyone explain the flag, IRQF_TRIGGER_NONE declared linux in the file,/kernel/linux/include/interrupt.h.
How can one use this flag?
IRQF_TRIGGER_NONE is defined with a bit-mask of 0 indicating that it does NOT imply any kind of edge or level triggered interrupt behaviour.
#define IRQF_TRIGGER_NONE 0x00000000
Hence registering an ISR using request_irq() with IRQF_TRIGGER_NONE does NOT modify the existing configuration of the IRQ. This is important in scenarios where we would simply like to register an ISR for an hardware in the mode it is currently configured [1].
Example usage of IRQF_TRIGGER_NONE in the Linux Kernel.
Our group is using a custom driver to interface four MAX3107 UARTs on a shared I2C bus. The interrupts of the four MAX3107's are connected (i.e. shared interrupt via logic or'ing)) to a GPIO pin on the ARM9 processor (LPC3180 module). When one or more of these devices interrupt, they pull the GPIO line, which is configured as a level-sensitive interrupt, low. My question concerns the need, or not, to disable the specific interrupt line in the handler code. (I should add that we are running Linux 2.6.10).
Based on my reading of several ARM-specific app notes on interrupts, it seems that when the ARM processor receives an interrupt, it automatically disables (masks?) the corresponding interrupt line (in our case this would seem to be the line corresponding to the GPIO pin we selected). If this is true, then it seems that we should not have to disable interrupts for this GPIO pin in our interrupt handler code as doing so would seem redundant (though it seems to work okay). Stated differently, it seems to me that if the ARM processor automatically disables the GPIO interrupt upon an interrupt occurring, then if anything, our interrupt handler code should only have to re-enable the interrupt once the device is serviced.
The interrupt handler code that we are using includes disable_irq_nosync(irqno); at the very beginning of the handler and a corresponding enable_irq() at the end of the handler. If the ARM processor has already disabled the interrupt line (in hardware), what is the effect of these calls (i.e. a call to disable_irq_nosync() followed by a call to enable(irq())?
From the Arm Information Center Documentation:
On entry to an exception (interrupt):
interrupt requests (IRQs) are disabled for all exceptions
fast interrupt requests (FIQs) are disabled for FIQ and Reset exceptions.
It then goes on to say:
Handling an FIQ causes IRQs and subsequent FIQs to be disabled,
preventing them from being handled until after the FIQ handler enables
them. This is usually done by restoring the CPSR from the SPSR at the
end of the handler.
So you do not have to worry about disabling them, but you do have to worry about re-enabling them.
You will need to include enable_irq() at the end of your routine, but you shouldn't need to disable anything at the beginning. I wouldn't think that calling disable_irq_nosync(irqno) in software after it has been called in hardware would effect anything. Since the hardware call is most definitely called before the software call has a chance to take over. But it's probably better to remove it from the code to follow convention and not confuse the next programmer who takes a look at it.
More info here:
Arm Information Center