On Thursday 12 September 2013 06:22 PM, Thomas Gleixner wrote: > On Thu, 12 Sep 2013, Santosh Shilimkar wrote: >> Specifically for the IRQ case addressed here, the cross-bar IP >> sits between the interrupt controller and peripheral interrupts. >> >> CPU <-- GIC <----- CROSSBAR <----- PERIPHERAL IRQs >> >> Just to expand it better, cross-bar input IRQ lines are more than >> what a GIC IRQ controller can support. >> e.q Total 250 peripheral IRQ lines out of which GIC support >> only 160 IRQ lines. >> >> So the idea here is to dynamically map the IRQ lines at >> cross-bar level to pick based on request_irq() so that one >> can optimize the use of limited IRQ lines at the GIC level. >> Strictly speaking the need is just establish the IRQ >> connection from peripheral to GIC and thats achieved >> at the request_irq() level. >> >> Earlier approach was to statically build this connections >> using the DT information in a separate driver probe but >> it had limitations of fixing the IRQ map and taking away >> flexibility what this IP provide. >> >> Hope this gives better picture to you behind the patch >> series. > > Yes. I halfways understand what you are trying to achieve. > > So CROSSBAR is a routing block between the peripheral and the GIC in > order to expand the number of possible interrupts. > > Now the real question is, how that expansion mechanism is supposed to > work. There are two possible scenarios: > > 1) Expand the number of handled interrupts beyond the GIC capacity: > > That requires a mechanism in CROSSBAR to map several CROSSBAR > interrupts to a particular GIC interrupt and provide a demux > mechanism to invoke the shared handlers. > This is not possible in hardware and not supported. Hardware has no notion of muxing multiple IRQ's to generate 1 IRQ or ack etc functionality. Its a simple MUX to tie knots between input and output wires. > 2) Provide a mapping mechanism between possibly 250 interrupt numbers > and a limitation of a total 160 active interrupts by the underlying > GIC. > This is the need and problem we are trying to solve. Regards, Santosh -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
