Am Freitag, den 11.05.2018, 13:39 +0100 schrieb Russell King - ARM Linux: > On Fri, May 11, 2018 at 05:07:37PM +0530, Pintu Kumar wrote: > > Hi, > > > > I need one help. > > I am using i.MX7 Sabre board with kernel version 4.1.15 > > > > Let's say I am interested in GPIO number: 21 > > I wanted to set CPU affinity for particular GPIO->IRQ number, so I > > tried the below steps: > > root@10:~# echo 21 > /sys/class/gpio/export > > root@10:~# echo "rising" > /sys/class/gpio/gpio21/edge > > root@10:~# cat /proc/interrupts | grep 21 > > 47: 0 0 gpio-mxc 21 Edge gpiolib > > root@10:~# cat /sys/class/gpio/gpio21/direction > > in > > root@10:~# cat /proc/irq/47/smp_affinity > > 3 > > root@10:~# echo 2 > /proc/irq/47/smp_affinity > > -bash: echo: write error: Input/output error > > > > But I get input/output error. > > When I debug further, found that irq_can_set_affinity is returning 0: > > [ 0.000000] genirq: irq_can_set_affinity (0): balance: 1, > > irq_data.chip: a81b7e48, irq_set_affinity: (null) > > [ 0.000000] write_irq_affinity: FAIL > > > > I also tried first setting /proc/irq/default_smp_affinity to 2 (from 3). > > This change is working, but the smp_affinity setting for the new IRQ > > is not working. > > > > When I try to set smp_affinity for mmc0, then it works. > > # cat /proc/interrupts | grep mmc > > 295: 55 0 GPCV2 22 Edge mmc0 > > 296: 0 0 GPCV2 23 Edge mmc1 > > 297: 52 0 GPCV2 24 Edge mmc2 > > > > root@10:~# echo 2 > /proc/irq/295/smp_affinity > > root@10:~# > > > > > > So, I wanted to know what are the conditions for which setting > > smp_affinity for an IRQ will work ? > > > > Is there any way by which I can set CPU affinity to a GPIO -> IRQ ? > > Whether, irq_set_affinity_hint() will work in this case ? > > IRQ affinity is only supported where interrupts are _directly_ wired to > the GIC. It's the GIC which does the interrupt steering to the CPU > cores. > > Interrupts on downstream interrupt controllers (such as GPCV2) have no > ability to be directed independently to other CPUs - the only possible > way to change the mapping is to move _all_ interrupts on that controller, > and any downstream chained interrupts at GIC level. > > Hence why Interrupt 295 has no irq_set_affinity function: there is no way > for the interrupt controller itself to change the affinity of the input > interrupt. The GPCv2 though is a secondary IRQ controller which has a 1:1 mapping of its input IRQs to the upstream GIC IRQ lines. Affinity can thus be handled by forwarding the request to the GIC by irq_chip_set_affinity_parent(). As this is handled correctly in the upstream kernel since the first commit introducing support for the GPCv2, it seems the issue is only present in some downstream kernel. Regards, Lucas _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
