device tree overlay phandle - linux-kernel

Question

I'm working on a Cyclone V SOC FPGA from Altera with a double Cortex-A9 processor. The embedded system (linux-socfpga 4.16) is created with Buildroot-2018.05.
I use a "top" device tree at boot time for processor component and a device-tree overlay to configure the FPGA part of the component and load the associated drivers. The overlay will be attach to the base_fpga_region of the top DT.
top device tree
/dts-v1/;
/ {
model = "MY_PROJECT"; /* appended from boardinfo */
compatible = "altr,socfpga-cyclone5", "altr,socfpga"; /* appended from boardinfo */
#address-cells = <1>;
#size-cells = <1>;
cpus {
[...]
}; //end cpus
memory {
device_type = "memory";
reg = <0xffff0000 0x00010000>,
<0x00000000 0x80000000>;
}; //end memory
reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
mem_dma_reserved {
compatible = "shared-dma-pool";
no-map;
reg = <0x78000000 0x8000000>;
};
};
soc: soc {
device_type = "soc";
ranges;
#address-cells = <1>;
#size-cells = <1>;
compatible = "altr,avalon", "simple-bus";
bus-frequency = <0>;
fpgabridge1: fpgabridge#1 {
compatible = "altr,socfpga-lwhps2fpga-bridge";
resets = <&hps_rstmgr 97>; /* appended from boardinfo */
clocks = <&l4_main_clk>; /* appended from boardinfo */
#address-cells = <1>;
#size-cells = <1>;
ranges;
bridge-enable = <1>;
label = "lwhps2fpga";
reset-names = "lwhps2fpga";
reg = <0xff200000 0x200000>;
reg-names = "axi_h2f_lw";
}; //end fpgabridge#1 (fpgabridge1)
base_fpga_region: base_fpga_region {
compatible = "fpga-region";
#address-cells = <0x2>;
#size-cells = <0x1>;
fpga-mgr = <&hps_fpgamgr>;
fpga-bridges = <&fpgabridge1>;
ranges = <0x0 0x0 0xff200000 0x200000>;
}; //end base_fpga_region (base_fpga_region)
etc......
Device tree overlay
/dts-v1/ /plugin/;
/{
fragment#0 {
target-path = "/soc/base_fpga_region";
#address-cells = <2>;
#size-cells = <1>;
__overlay__ {
#address-cells = <2>;
#size-cells = <1>;
firmware-name = "my_project.rbf";
my_dma_0: dma#0x000000000 {
compatible = "my_company,my_dma-0.1";
reg = <0x00000000 0x0000000 0x00000014>;
memory-region = <&mem_dma_reserved>;
}; //end dma#0x000000000 (my_dma_0)
};
};
};
my problem is to link the mem_dma_reserved from the top DT to the memory-region in the overlay.
I assume that while converting dts to dtbo with the -# option, the overlay shall get the phandle for mem_dma_reserved with the __fixups__ option. I've created the dtbo file and converted it again in dts to see what is done during the compilation :
dtc -# -I dts -O dtb -o overlay.dtbo overlay.dts
dtc -I dtb -O dts -o overlay_recovery.dts overlay.dtbo
device tree overlay regenerated
/dts-v1/;
/ {
fragment#0 {
target-path = "/soc/base_fpga_region";
#address-cells = <0x2>;
#size-cells = <0x1>;
__overlay__ {
#address-cells = <0x2>;
#size-cells = <0x1>;
firmware-name = "my_project.rbf";
dma#0x000000000 {
compatible = "my_company,my_dma-0.1";
reg = <0x0 0x0 0x14>;
memory-region = <0xffffffff>; // phandle converted to 0xffffffff, cannot resolve unless the __fixup__ function does it.
linux,phandle = <0x2>;
phandle = <0x2>;
};
};
};
__symbols__ {
my_dma_0 = "/fragment#0/__overlay__/dma#0x000000000";
};
__fixups__ {
mem_dma_reserved = "/fragment#0/__overlay__/dma#0x000000000:memory-region:0";
};
};
We can see that the phandle for the memory-region is 0xFFFFFFFF because the overlay doesn't know about the <&mem_dma_reserved> node. the fixup part shall be able to get back the phandle at loading time, but it isn't working and I get this error :
[ 27.434730] OF: resolver: of_resolve_phandles: no symbols in root of device tree.
[ 27.440401] OF: resolver: overlay phandle fixup failed: -22
[ 27.445993] create_overlay: Failed to resolve tree
I have made the same regeneration from dtb to dts on the top DT. I have seen that the phandle of the reserved memory is actually 0x6. I have written <0x6> instead of <&mem_dma_reserved> in the device tree overlay and with this configuration, everything loads !
How can I make the overlay find the <&mem_dma_reserved> automatically without doing it by hand ?
EDIT
As pointed by ikwzm I have added in the top device tree the following lines :
reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
mem_dma_reserved: mem_dma_reserved { // add a label
compatible = "shared-dma-pool";
no-map;
reg = <0x78000000 0x8000000>;
};
};
[...]
// add the whole symbol block
__symbols__ {
mem_dma_reserved = "/reserved-memory/mem_dma_reserved ";
};
The errors are now gone, but :
I was expecting the driver for my_dma to be loaded during the operation.
I checked that the device tree overlay is well taken into account with :
ls /sys/firmware/devicetree/base/soc/base_fpga_region/
my_dma_0
other_stuff
cat /sys/firmware/devicetree/base/soc/base_fpga_region/my_dma_0/memory-region
//nothing//
The memory region doesn't seem to be attached.
What I have missed ?

Answer 1

When making the top dtb, did you attach the option --symbol (or -#) to the dtc command?
Add a label (symbol) to mem_dma_reserved as follows.
reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
mem_dma_reserved: mem_dma_reserved {
compatible = "shared-dma-pool";
no-map;
reg = <0x78000000 0x8000000>;
};
};
When dtb is created with the --symbol option dtc command, __symbols__{...}; is added as follows, and mem_dma_reserved = "/reserved-memory/ mem_dma_reserved"; should be found in it.
__symbols__ {
:
:
:
mem_dma_reserved = "/reserved-memory/mem_dma_reserved";
usb_phy0 = "/phy0";
};