Re: [Xen-devel] [RFC] Add support for Xen ARM guest on FreeBSD

[Nathan Whitehorn <nwhitehorn@xxxxxxxxxxx>]

On 01/18/14 20:44, Warner Losh wrote:
> On Jan 18, 2014, at 4:41 PM, Julien Grall wrote:
>
>> Hello Nathan,
>>
>> On 01/17/2014 03:04 AM, Nathan Whitehorn wrote:
>>> On 01/16/14 18:36, Julien Grall wrote:
>>>>
>>>> On 01/16/2014 01:56 AM, Nathan Whitehorn wrote:
>>>> As I understand, only the simple bus code (see simplebus_attach) is
>>>> translating the interrupts in the device on a resource.
>>>> So if you have a node directly attached to the root node with
>>>> interrupts and MMIO, the driver won't be able to retrieve and
>>>> translate the interrupts via bus_alloc_resources.
>>> Why not? nexus on ARM, MIPS, PowerPC, and sparc64 can do this.
>> I have digged into the code to find the reason of my issue. FreeBSD is 
>> receiving a VM fault when the driver (xen-dt) is trying to setup the IRQ.
>>
>> This is because the GIC is not yet initialized but FreeBSD asks to unmask 
>> the IRQ (sys/arm/arm/gic.c:306).
>>
>> With this problem, all device nodes that are before the GIC in the device 
>> tree can't have interrupts. For instance this simple device will segfault on 
>> FreeBSD:
>>
>> / {
>>
>>  mybus {
>>     compatible = "simple-bus";
>>
>>     mynode {
>>        interrupt-parent = &gic;
>>        interrupts = <...>;
>>     };
>>
>>     gic: gic@xxxx {
>>        interrupt-controller;
>>     }
>>  };
>> };
>>
>> The node "mynode" will have to move after the GIC to be able to work 
>> correctly.
> This stems from a difference in enumeration between FreeBSD and Linux. 
> FreeBSD enumerates the devices in DTB order, while Linux does a partial 
> ordering based on dependencies.
>
> Warner

Enumerating in some other order doesn't necessarily help: since the
interrupt and bus trees are independent, circular dependencies can
happen. This is not a hypothetical: on most powermacs, the main
interrupt controller is a functional unit on a PCI device -- a PCI
device whose other units have interrupt lines that eventually connect
back to itself. There is no way to fix that with ordering. So I think we
still need to defer interrupt setup. It's not that bad -- PPC already
does this to handle the powermac case.
-Nathan

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