Re: Using DT overlays for adding virtual hardware

[Pantelis Antoniou <pantelis.antoniou@konsulko.com>]

Hi Jan,

> On Jun 21, 2016, at 13:13 , Jan Kiszka <jan.kiszka@siemens.com> wrote:
> 
> Hi Pantelis,
> 
> coming back to this topic:
> 
> On 2016-06-09 08:03, Jan Kiszka wrote:
>> OK, trial and error, and some interesting insights: I've played with DT
>> fragments and the overlay configfs patch of Pantelis [1] to have a
>> convenient start. Interestingly, I wasn't able to load a fragment that
>> followed the format specification for overlays ("Failed to resolve
>> tree"). By chance, I got this one working:
>> 
>> /dts-v1/;
>> / {
>> 	fragment {
>> 		target-path = "/soc@01c00000";
>> 		__overlay__ {
>> 			#address-cells = <2>;
>> 			#size-cells = <2>;
>> 
>> 			vpci@0x2000000 {
>> 				compatible = "pci-host-cam-generic";
>> 				device_type = "pci";
>> 				#address-cells = <3>;
>> 				#size-cells = <2>;
>> 				reg = <0 0x2000000 0 0x1000000>;
>> 				ranges =
>> 					<0x02000000 0x00 0x10000000 0x00 0x10000000 0x00 0x30000000>;
>> 			};
>> 		};
>> 	};
>> };
>> 
>> It successfully makes a BananaPi kernel add a pci host with the
>> specified config space and MMIO window.
>> 
>> [   81.619583] PCI host bridge /soc@01c00000/vpci@0x2000000 ranges:
>> [   81.619610]   No bus range found for /soc@01c00000/vpci@0x2000000, using [bus 00-ff]
>> [   81.619634]   MEM 0x10000000..0x3fffffff -> 0x10000000
>> [   81.620482] pci-host-generic 2000000.vpci: ECAM at [mem 0x02000000-0x02ffffff] for [bus 00-ff]
>> [   81.620779] pci-host-generic 2000000.vpci: PCI host bridge to bus 0000:00
>> [   81.620801] pci_bus 0000:00: root bus resource [bus 00-ff]
>> [   81.620814] pci_bus 0000:00: root bus resource [mem 0x10000000-0x3fffffff]
>> [   81.620851] PCI: bus0: Fast back to back transfers enabled
>> 
>> So, no /plugin/ statement, no phandles resolution. This format even
>> builds with the in-kernel dtc. Any explanations? Does the code make
>> sense (at least it builds without warnings)?
>> 
>> Now I need to back this with some code in Jailhouse.
> 
> Meanwhile I got a virtual PCI device recognized by Linux when running
> over Jailhouse. However, my hack above doesn't get me to proper
> interrupt mapping yet. This is what I was trying with upstream dtc:
> 
> /dts-v1/;
> / {
> 	compatible = "lemaker,bananapi", "allwinner,sun7i-a20";
> 
> 	fragment@0 {
> 		target-path = "/soc@01c00000";
> 		__overlay__ {
> 			#address-cells = <2>;
> 			#size-cells = <2>;
> 
> 			vpci@2000000 {
> 				compatible = "pci-host-ecam-generic";
> 				device_type = "pci";
> 				bus-range = <0 0>;
> 				#address-cells = <3>;
> 				#size-cells = <2>;
> 				#interrupt-cells = <1>;
> 				interrupt-map-mask = <0 0 0 7>;
> 				interrupt-map = <0 0 0 1 &gic 0 0 0 123 4>,
> 						<0 0 0 2 &gic 0 0 0 124 4>,
> 						<0 0 0 3 &gic 0 0 0 125 4>,
> 						<0 0 0 4 &gic 0 0 0 126 4>;
> 				reg = <0 0x2000000 0 0x100000>;
> 				ranges =
> 					<0x02000000 0x00 0x10000000 0x00 0x10000000 0x00 0x30000000>;
> 			};
> 		};
> 	};
> 
> 	gic: fragment@1 {
> 		target-path = "/soc@01c00000/interrupt-controller@01c81000";
> 		__overlay__ {
> 		};
> 	};
> };
> 

^ This is not going to work: You need the reference to the real gic not the empty fragment
here that has a target there.

You need to compile with the correct dtc, and you also need to compile the base dts
with dtc too, using the -@ flag. You can hack around it by adding something like

__symbols__ {
	gic = "/soc@01c00000/interrupt-controller@01c81000”;
};

But you really need the __symbols__ node of the base dts generated by the dtc proper cause
the above is a dirty hack.


> And this is what Linux detects on that PCI bus:
> 
> 00:0f.0 RAM memory: Red Hat, Inc Inter-VM shared memory
>        Subsystem: Red Hat, Inc Inter-VM shared memory
>        Control: I/O- Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
>        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
>        Interrupt: pin A routed to IRQ 17
>        Region 0: Memory at 10000000 (64-bit, non-prefetchable) [size=256]
>        Region 4: Memory at 10000100 (64-bit, non-prefetchable) [size=32]
>        Kernel modules: ivshmem_net
> 
> However, registering a handler on IRQ 17 fails (-EINVAL).
> 
> 
> With your dtc [2] (dtc -@ -I dts -O dtb -o vpci-bpi.dtb vpci-bpi.dts)
> and this fragment, I'm still not able to load the blob:
> 
> /dts-v1/;
> /plugin/;
> / {
> 	compatible = "lemaker,bananapi", "allwinner,sun7i-a20";
> 
> 	fragment@0 {
> 		target-path = "/soc@01c00000";
> 		__overlay__ {
> 			#address-cells = <2>;
> 			#size-cells = <2>;
> 
> 			vpci@2000000 {
> 				compatible = "pci-host-ecam-generic";
> 				device_type = "pci";
> 				bus-range = <0 0>;
> 				#address-cells = <3>;
> 				#size-cells = <2>;
> 				#interrupt-cells = <1>;
> 				interrupt-map-mask = <0 0 0 7>;
> 				interrupt-map = <0 0 0 1 &gic 0 0 0 123 4>,
> 						<0 0 0 2 &gic 0 0 0 124 4>,
> 						<0 0 0 3 &gic 0 0 0 125 4>,
> 						<0 0 0 4 &gic 0 0 0 126 4>;
> 				reg = <0 0x2000000 0 0x100000>;
> 				ranges =
> 					<0x02000000 0x00 0x10000000 0x00 0x10000000 0x00 0x30000000>;
> 			};
> 		};
> 	};
> };
> 

Please try this branch of dtc; it’s a wip of what I’m trying to push to upstream.

https://github.com/pantoniou/dtc/tree/dgibson-overlay-panto

> Any suggestions? Any patches I'm missing in upstream to make that work?
> 
> Jan
> 

Regards

— Pantelis

> [1] https://github.com/pantoniou/linux-beagle-track-mainline/commit/160e68ec89eca33e8ed0abb13d52c07c54d7fc10
> [2] https://github.com/pantoniou/dtc/tree/dgibson-overlay-panto
> 
> -- 
> Siemens AG, Corporate Technology, CT RDA ITP SES-DE
> Corporate Competence Center Embedded Linux