Re: [Xen-users] i2c pass-through in mpsoc

[Julien Grall <julien.grall@xxxxxxx>]

On 24/10/17 07:45, Jesús Lázaro wrote:
> Hi,
Hello,

Please avoid top-posting. I am CC-ing Edgar who might also be able to 
give some feedback here.
> I had a typo in my previous message.
>
> Dom0 has Xen support and I am able to launch different DomU.
>
> DomU has also Xen support for guests following:
> https://wiki.xenproject.org/wiki/Mainline_Linux_Kernel_Configs
>
> Dom0 has knowledge, through the device tree, about the I2C but appears 
> as disabled and with xen,passthough property.
> If instead of launching Dom0 as primary OS, I launch DomU (they both are 
> very similar), with the I2C in the DT to okay, it appears and can be 
> used, so I2C support is built into the kernel.
> The issue is that when being launch as DomU from Dom0, the i2c device 
> does not appear. The main difference is that when in non Xen 
> environment, the i2c is in the amba bus but when in Xen environment, it 
> is in the pass-through simple bus.
I am not sure what you mean here. When I looked at the mpsoc DT 
(xilinx/zynqmp.dtsi), the i2c is indeed under a node called amba.
But the name of the node is irrelevant here. However the compatible 
string is "simple-bus" as used in the partial device-tree below.
Did I miss anything?

> The passed devicetree is:
>
> /dts-v1/;
> / {
>     #address-cells = <0x2>;
>     #size-cells = <0x2>;
>
>
>      passthrough {
>          compatible = "simple-bus";
>          ranges;
>          #address-cells = <0x2>;
>          #size-cells = <0x2>;
>
>          misc_clk {
>                  #clock-cells = <0x0>;
>                  clock-frequency = <0x7735940>;
>                  compatible = "fixed-clock";
>                  linux,phandle = <0x2>;
>                  phandle = <0x2>;
>          };
>
>          pd-i2c1 {
>                  #power-domain-cells = <0x0>;
This not does not contain any compatible string. Is it normal?

>                  pd-id = <0x26>;
>                  linux,phandle = <0x1>;
>                  phandle = <0x1>;
>          };
>
>
>          i2c@ff030000 {
>                  compatible = "cdns,i2c-r1p14", "cdns,i2c-r1p10";
>                  status = "okay";
>                  interrupts = <0x0 0x12 0x4>;
>                  reg = <0x0 0xff030000 0x0 0x1000>;
>                  #address-cells = <0x1>;
>                  #size-cells = <0x0>;
>                  power-domains = <0x1>;
>                  clocks = <0x3 0x3e>;
>                  clock-frequency = <0x61a80>;
>          };
>      };
> };
>
> The final result is that it does not load the i2c module and does not 
> create the i2c device. It looks like, since it does not find any i2c in 
> the amba, does not bother to load the module. There are not I2C related 
> messages in none of the dmesgs (Dom0, DomU).
>
> Regards,
>
> Jesús
>
> On 23/10/17 12:57, Julien Grall wrote:
> > On 13/10/17 10:55, Jesús Lázaro wrote:
> > > Hi,
> > Hello,
> >
> > > Avoiding the dtdev property avoids any error. Now the issue is that, 
> > > although in the devicetree/passthrough section the i2c appears, the 
> > > kernel fails to load any drivers and does not create the /dev/i2c 
> > > device.
> > > The dom0 kernel has XEN support following 
> > > https://wiki.xenproject.org/wiki/Mainline_Linux_Kernel_Configs
> > > dmesg does not offer any messages regarding issues with the i2c.
> > I am a bit confused. You say you pass-through to a guest, but speak 
> > about Dom0 kernel. So the dmesg is from DomU or Dom0?
> > Note that when doing platform device passthrough, Dom0 kernel is not 
> > involved in the process. The guest will have full access and should 
> > detect it via device-tree.
> > Make sure you have I2C built in your guest kernel.
> >
> > Cheers,
--
Julien Grall

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