On Thu, 29 Nov 2012, anish kumar wrote: > On Wed, 2012-11-28 at 20:10 +0530, manty kuma wrote: > > In linux interrupt programming, we do request_irq(...) in this > > function, the first argument is irq number. If i am not wrong, this is > > the interrupt line that we are requesting from kernel. For one > Right. > > particular hardware, is this IRQ line fixed or can it register on any > > line based on the availability? The concept is not clear. Kindly > In linux there are two concepts related to interrupt which is never > clearly mentioned anywhere(at least not that I know of) and that is why > let me clarify.
Documentation/IRQ-domain.txt > 1. Hardware interrupt number.Given by your irq controller or the > hardware which is capable of generating the interrupts. > 2. Software interrupt number assigned by linux interrupt handling core. > > So the first question which arises in mind is: why does linux generates > the software interrupt number?Won't hardware interrupt number be enough > to keep everyone happy? > > Simple reason is just for book keeping as the software interrupt numbers > generated would be linear as we are in control of what numbers to > allocate and if we start using the numbers generated by irq controller > which can generate random numbers then searching and indexing would > require expensive operations as compared to working in linear > domain(experts can add more here if I am not to the point). > > However if your irq controller is capable of choosing the interrupt > numbers then linux irq number will be same as hardware interrupt number. > > So let's come back to the question.So for a particular hardware the > hardware interrupt line would be always fixed as well as the software > interrupt numbers generated by the linux irq core. > > > explain. Also, when i do interrupt programming for AVR or ARM, all > > the peripherals are having fixed IRQ numbers. and they are having > > handlers. There is no concept of interrupt lines as such. So my > > second question is how are IRQ lines and IRQ numbers related? > IRQ lines are connected to irq controller and you should have a look at > the driver of your irq controller as to how does it assign the hardware > irq numbers(probably by reading some registers).All the peripherals are > connected to the irq controller such as keyboard and mouse and they have > fixed irq lines.Once a signal is asserted the irq controller raises an > interrupt to arm core and arm core in turn raises a hardware > interrupt.This hardware interrupt will call into linux irq handling > code.Which interrupt handler to be called is already decided by the > individual drivers, remember they have called request_irq with an > interrupt number. > This interrupt number would be a software interrupt number as explained > before and this number to hardware interrupt number association is done > by the interrupt controller or the chip driver which is capable of > taking(handling) one interrupt and calling individual interrupt handlers > after reading the corresponding registers(read handle_nested_irq). > This conversion of hardware interrupt number to software interrupt > number is done in /kernel/irq/irqdomain.c file. > > PS:I may be wrong but this description is from what I have read in the > code.Please do point out any mistakes. > > > > > > Thanks, > > Sandeep > > _______________________________________________ > > Kernelnewbies mailing list > > kernelnewb...@kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > -- Lee Jones Linaro ST-Ericsson Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
