How to make and apply device tree overlays for the kernel

[kunohel]

``Hi,

I'm using an Orin Nano and I would like to add an extra property to one of the pcie root ports nvidia,disable-power-down, but I struggle a bit to make it work.

Currently my linux-tegra_%.bbappend looks like the following:

FILESEXTRAPATHS:prepend := "${THISDIR}/files:"

SRC_URI:append = " \
    file://overlay.cfg \
    file://pcie-disable-power-down.dts;subdir=git/arch/${ARCH}/boot/dts/nvidia \
"

KERNEL_DEVICETREE:append = " nvidia/pcie-disable-power-down.dtb"
KERNEL_DEVICETREE_APPLY_OVERLAYS:append = " nvidia/pcie-disable-power-down.dtb"

# KERNEL_EXTRA_ARGS:append = " DTC_FLAGS='-@'"

And my dts;

/dts-v1/;

/ {
    pcie@141e0000 {
        nvidia,disable-power-down;
    };
    pcie_ep@141e0000 {
        nvidia,disable-power-down;
    };
};

It compiles but is not applied in Linux;

root@user:~# ls /proc/device-tree/pcie\@141e0000/                                                                                     
#address-cells                       nvidia,aspm-pwr-on-t                                                                                  
#interrupt-cells                     nvidia,aspm-pwr-on-t-us                                                                               
#size-cells                          nvidia,aux-clk-freq                                                                                   
bus-range                            nvidia,bpmp                                                                                           
clock-names                          nvidia,cap-pl16g-cap-off                                                                              
clocks                               nvidia,cap-pl16g-status                                                                               
compatible                           nvidia,cfg-link-cap-l1sub                                                                             
device_type                          nvidia,controller-id                                                                                  
dma-coherent                         nvidia,disable-aspm-states                                                                            
interconnect-names                   nvidia,disable-l1-cpm                                                                                 
interconnects                        nvidia,dl-feature-cap                                                                                 
interrupt-map                        nvidia,dvfs-tbl                                                                                       
interrupt-map-mask                   nvidia,event-cntr-ctrl                                                                                
interrupt-names                      nvidia,event-cntr-data                                                                                
interrupts                           nvidia,max-speed                                                                                      
iommu-map                            nvidia,preset-init                                                                                    
iommu-map-mask                       nvidia,ptm-cap-off                                                                                    
iommus                               nvidia,tsa-config                                                                                     
linux,pci-domain                     phandle                                                                                               
max-link-speed                       phy-names                                                                                             
msi-map                              phys                                                                                                  
msi-parent                           power-domains                                                                                         
name                                 ranges                                                                                                
num-lanes                            reg                                                                                                   
num-viewport                         reg-names                                                                                             
nvidia,aspm-cmrt                     reset-names                                                                                           
nvidia,aspm-cmrt-us                  resets                                                                                                
nvidia,aspm-l0s-entrance-latency     status                                                                                                
nvidia,aspm-l0s-entrance-latency-us  vddio-pex-ctl-supply

I have also tried to use fragments in my dts, but this fails on do_apply_devicetree_overlays:

/dts-v1/;
/plugin/;

/ {
    fragment@100 {
        target-path = "/";
        __overlay__ {
            pcie@141e0000 {
                nvidia,disable-power-down;
            };
            pcie_ep@141e0000 {
                nvidia,disable-power-down;
            };
        };
    };
};

How can I get this to work?

[kunohel]

I figured it out how to properly apply the property to the pcie node.
Solution:

.bbapend file:

FILESEXTRAPATHS:prepend := "${THISDIR}/files:"

SRC_URI:append = " \
    file://overlay.cfg \
    file://pcie-disable-power-down.dts;subdir=git/arch/${ARCH}/boot/dts/nvidia \
"

KERNEL_DEVICETREE_APPLY_OVERLAYS:append = " nvidia/pcie-disable-power-down.dtb"

.dts file:

/dts-v1/;
/plugin/;

/ {
    compatible = "nvidia,tegra234-pcie", "nvidia,p3768-0000+p3767-0003", "nvidia,p3768-0000+p3767-0005", "nvidia,p3767-0003", "nvidia,p3767-0005", "nvidia,tegra234", "nvidia,tegra23x";
    fragment@100 {
        target-path = "/";
        __overlay__ {
            pcie@141e0000 {
                nvidia,disable-power-down;
            };
        };
    };
};