Regarding FPGA based cascaded PIC

thirumalai.p thirumalai.p at
Thu Nov 5 13:46:40 EST 2009

On Thu, 05 Nov 2009 07:51:22 +1100, Benjamin Herrenschmidt
<benh at> wrote:
> On Wed, 2009-11-04 at 18:09 +0530, Thirumalai wrote:
>> you understood correctly. Here the problem lies.Correct me if i am
>> So
>> you are telling that irq_of_parse_and_map() will invoke the map/xlate of
>> my
>> FPGA pic. Right.
>> But this is what not happening. Instead of calling my map/xlate
>> the irq_of_parse_and_map() function is invoking mpic's map/xlate
>> function.
> irq_of_parse_and_map() will call the map/xlate function of the parent
> PIC for the given interrupt.
> In your case, the interrupts you are calling it for are defined as being
> interrupts wiring the FPGA to the MPIC, hence are MPIC inputs, and thus
> will be parsed/mapped by the MPIC. From the MPIC standpoint, the FPGA is
> just a device.
> So the code is doing what you tell it to do :-)
> I don't understand what you are actually trying to acheive. If those 3
> interrupts aren't outputs from the FPGA to the MPIC but input to the
> FPGA then they shouldn't be there, they should be device interrupts
> connected to the FPGA. Those will end up with map/xlate called in the
> FPGA host.
I Understood the thing. Thank you very much. So you mean to say that my
map/xlate functions will get invoked only for the devices which is
connected the FPGA PIC. So for example suppose if i have an WDT connected
to my FPGA then the interrupt-parent tag should point to FPGA-PIC. So at
that time the irq_of_parse_and_map() will invoke my map/xlate functions

So i need to define the nodes on my device tree for the devices which are
all going to generate interrupts for FPGA and keeping the interrupt-parent
property as fpga-pic.

So my device node for WDT is something like the following

                    wdt at 4,2000 {
                       #interrupt-cells = <2>;
                       device_type = "watchdog";
                       compatible = "gef,fpga-wdt";
                       reg = <0x4 0x2000 0x8>;
                       interrupts = <0x1a 0x4>;
                       interrupt-parent = <&fpga_pic>;
Correct me if i am wrong.

> Ben.
>> Here is the piece of code that we are using.
>> fpga_pic_irq_host = irq_alloc_host(pic, IRQ_HOST_MAP_LINEAR,
>>                         DPVPX0659_FPGA_NUM_IRQS,&fpga_pic_host_ops,
>>                         NO_IRQ);
>>         if (fpga_pic_irq_host == NULL) {
>>                 printk("FPGA PIC: Unable to allocate host\n");
>>                 return;
>>         }
>>         for (i = 0; i < 3; i++) {
>>                 fpga_irqs[i] = irq_of_parse_and_map(pic, i);
>>                 if (fpga_irqs[i] == NO_IRQ) {
>>                         printk("FPGA PIC: can't get irq %d.\n", i);
>>                         continue;
>>                 }
>>                 printk("interrupt from device tree : %d
>>                 \n",fpga_irqs[i]);
>>         }
Thank you

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