Date: Sat, 18 Jan 2014 21:01:17 -0600 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: Warner Losh <imp@bsdimp.com>, Julien Grall <julien.grall@linaro.org> Cc: ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, xen-devel@lists.xen.org, freebsd-xen@freebsd.org, freebsd-arm@FreeBSD.org, gibbs@freebsd.org Subject: Re: [RFC] Add support for Xen ARM guest on FreeBSD Message-ID: <52DB3FFD.2070503@freebsd.org> In-Reply-To: <3AE8EDE6-D931-4F93-9BF7-ABFB297B5B96@bsdimp.com> References: <1389733267-20822-1-git-send-email-julien.grall@linaro.org> <24851B79-7EC7-4E3A-94DB-4B9B86FDFFFC@bsdimp.com> <52D6B62A.9000208@linaro.org> <52D73C4E.2080306@freebsd.org> <52D87B15.5090208@linaro.org> <52D89DC9.7050303@freebsd.org> <52DB1138.6010804@linaro.org> <3AE8EDE6-D931-4F93-9BF7-ABFB297B5B96@bsdimp.com>
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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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