[FAQ] TMDX654IDKEVM: Turning off unused cores

Hi Rei,

We options to hotplug CPUs from Linux.

root@am65xx-evm:~# echo 0 > /sys/devices/system/cpu/cpu2/online
[ 36.430636] IRQ42: set affinity failed(-22).
[ 36.434914] IRQ43: set affinity failed(-22).
[ 36.439176] IRQ45: set affinity failed(-22).
[ 36.443577] IRQ202: set affinity failed(-22).
[ 36.447926] IRQ203: set affinity failed(-22).
[ 36.453330] process 183 (rngd) no longer affine to cpu2
[ 36.454283] CPU2: shutdown
[ 36.462287] psci: CPU2 killed (polled 0 ms)

root@am65xx-evm:~# echo 0 > /sys/devices/system/cpu/cpu3/online
[ 41.606562] IRQ 8: no longer affine to CPU3
[ 41.610756] IRQ 10: no longer affine to CPU3
[ 41.615021] IRQ 12: no longer affine to CPU3
[ 41.619288] IRQ 18: no longer affine to CPU3
[ 41.623553] IRQ 22: no longer affine to CPU3
[ 41.627817] IRQ 24: no longer affine to CPU3
[ 41.632080] IRQ 26: no longer affine to CPU3
[ 41.636343] IRQ 28: no longer affine to CPU3
[ 41.640606] IRQ 30: no longer affine to CPU3
[ 41.644869] IRQ 32: no longer affine to CPU3
[ 41.649155] IRQ42: set affinity failed(-22).
[ 41.653415] IRQ43: set affinity failed(-22).
[ 41.657676] IRQ45: set affinity failed(-22).
[ 41.662080] IRQ202: set affinity failed(-22).
[ 41.666428] IRQ203: set affinity failed(-22).
[ 41.671836] process 184 (rngd) no longer affine to cpu3
[ 41.671963] CPU3: shutdown
[ 41.681553] psci: CPU3 killed (polled 0 ms)

Now we see that interrupts are only for CPU0/1 which are active.

root@am65xx-evm:~# cat /proc/interrupts
CPU0 CPU1
3: 28415 49412 GICv3 30 Level arch_timer
6: 0 0 GICv3 23 Level arm-pmu
7: 17 0 GICv3 728 Level 42120000.i2c
8: 0 0 GICv3 596 Level 40b00000.i2c
9: 0 0 GICv3 592 Level 40300000.spi
10: 0 0 GICv3 593 Level 40310000.spi
11: 0 0 GICv3 594 Level 40320000.spi
12: 0 0 GICv3 612 Level TI-am335x-adc.0.auto
13: 0 0 GICv3 613 Level TI-am335x-adc.1.auto
18: 0 0 GICv3 585 Level 47050000.spi
19: 792 0 GICv3 224 Level 2800000.serial
22: 42 0 GICv3 232 Level 2000000.i2c
23: 1 0 GICv3 233 Level 2010000.i2c
24: 0 0 GICv3 234 Level 2020000.i2c
25: 0 0 GICv3 235 Level 2030000.i2c
26: 0 0 GICv3 216 Level 2100000.spi
27: 0 0 GICv3 217 Level 2110000.spi
28: 0 0 GICv3 218 Level 2120000.spi
29: 0 0 GICv3 219 Level 2130000.spi
30: 0 0 GICv3 220 Level 2140000.spi
31: 270 0 GICv3 168 Level mmc0
32: 7635 0 GICv3 169 Level mmc1
35: 704 0 GICv3 69 Level 32c00000.mailbox thr_011
36: 0 0 GICv3 372 Edge ks-pcie-error-irq
37: 0 0 GICv3 184 Level cal
38: 2 0 GICv3 194 Level SGX ISR
41: 0 0 ITS-MSI 0 Edge PCIe PME, aerdrv
42: 0 0 MSI-INTA 12779616 Level 285c0000.dma-controller chan0
43: 0 0 MSI-INTA 12779617 Level 46000000.ethernet-tx0
45: 0 0 MSI-INTA 12779619 Level 46000000.ethernet
202: 0 0 MSI-INTA 12255536 Level 31150000.dma-controller chan0
203: 0 0 MSI-INTA 12255537 Level 31150000.dma-controller chan1
666: 0 0 INTR 391 Level 310d0000.cpts
695: 0 0 GPIO 24 Edge -davinci_gpio GPIO Key USER1
696: 0 0 GPIO 25 Edge -davinci_gpio 0-0039
698: 0 0 GPIO 27 Edge -davinci_gpio GPIO Key USER2
925: 3 0 INTR 436 Level mbox-mcu-r5fss0-core0
1291: 0 0 GICv3 602 Level 46000000.ethernet
1292: 0 0 GICv3 132 Level xhci-hcd:usb1
1295: 0 0 GICv3 148 Level dwc3-otg
IPI0: 1713 2488 Rescheduling interrupts
IPI1: 559 276 Function call interrupts
IPI2: 0 0 CPU stop interrupts
IPI3: 0 0 CPU stop (for crash dump) interrupts
IPI4: 0 0 Timer broadcast interrupts
IPI5: 0 0 IRQ work interrupts
IPI6: 0 0 CPU wake-up interrupts
Err: 0

If you want compile time disabling can you try below diff:

diff --git a/arch/arm64/boot/dts/ti/k3-am654.dtsi b/arch/arm64/boot/dts/ti/k3-am654.dtsi
index b221abf43..1c4325caa 100644
--- a/arch/arm64/boot/dts/ti/k3-am654.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-am654.dtsi
@@ -60,34 +60,6 @@
                        d-cache-sets = <128>;
                        next-level-cache = <&L2_0>;
                };
-
-               cpu2: cpu@100 {
-                       compatible = "arm,cortex-a53";
-                       reg = <0x100>;
-                       device_type = "cpu";
-                       enable-method = "psci";
-                       i-cache-size = <0x8000>;
-                       i-cache-line-size = <64>;
-                       i-cache-sets = <256>;
-                       d-cache-size = <0x8000>;
-                       d-cache-line-size = <64>;
-                       d-cache-sets = <128>;
-                       next-level-cache = <&L2_1>;
-               };
-
-               cpu3: cpu@101 {
-                       compatible = "arm,cortex-a53";
-                       reg = <0x101>;
-                       device_type = "cpu";
-                       enable-method = "psci";
-                       i-cache-size = <0x8000>;
-                       i-cache-line-size = <64>;
-                       i-cache-sets = <256>;
-                       d-cache-size = <0x8000>;
-                       d-cache-line-size = <64>;
-                       d-cache-sets = <128>;
-                       next-level-cache = <&L2_1>;
-               };
        };
 

Best Regards,
Keerthy