Re: [PATCH v6 2/7] xen/arm: add pci-domain for disabled devices

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 22.11.21 17:29, Julien Grall wrote:
>
>
> On 18/11/2021 07:13, Oleksandr Andrushchenko wrote:
>> Hi, Julien!
>
> Hi Oleksandr,
>
>> On 17.11.21 23:33, Julien Grall wrote:
>>> Hi Oleksandr,
>>>
>>> On 17/11/2021 06:56, Oleksandr Andrushchenko wrote:
>>>> Hi, Julien!
>>>>
>>>> On 16.11.21 20:48, Julien Grall wrote:
>>>>> Hi Oleksander,
>>>>>
>>>>> On 05/11/2021 06:33, Oleksandr Andrushchenko wrote:
>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>>>>
>>>>>> If a PCI host bridge device is present in the device tree, but is
>>>>>> disabled, then its PCI host bridge driver was not instantiated.
>>>>>> This results in the failure of the pci_get_host_bridge_segment()
>>>>>> and the following panic during Xen start:
>>>>>>
>>>>>> (XEN) Device tree generation failed (-22).
>>>>>> (XEN)
>>>>>> (XEN) ****************************************
>>>>>> (XEN) Panic on CPU 0:
>>>>>> (XEN) Could not set up DOM0 guest OS
>>>>>> (XEN) ****************************************
>>>>>>
>>>>>> Fix this by adding "linux,pci-domain" property for all device tree nodes
>>>>>> which have "pci" device type, so we know which segments will be used by
>>>>>> the guest for which bridges.
>>>>>>
>>>>>> Fixes: 4cfab4425d39 ("xen/arm: Add linux,pci-domain property for hwdom 
>>>>>> if not available.")
>>>>>>
>>>>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>>>>
>>>>>> ---
>>>>>> New in v6
>>>>>> ---
>>>>>>     xen/arch/arm/domain_build.c        | 15 ++++++++++++++-
>>>>>>     xen/arch/arm/pci/pci-host-common.c |  2 +-
>>>>>>     xen/include/asm-arm/pci.h          |  8 ++++++++
>>>>>>     3 files changed, 23 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
>>>>>> index 491f5e2c316e..f7fcb1400c19 100644
>>>>>> --- a/xen/arch/arm/domain_build.c
>>>>>> +++ b/xen/arch/arm/domain_build.c
>>>>>> @@ -753,9 +753,22 @@ static int __init write_properties(struct domain 
>>>>>> *d, struct kernel_info *kinfo,
>>>>>>             {
>>>>>>                 uint16_t segment;
>>>>>>     +            /*
>>>>>> +             * The node doesn't have "linux,pci-domain" property and it 
>>>>>> is
>>>>>> +             * possible that:
>>>>>> +             *  - Xen only has drivers for a part of the host bridges
>>>>>> +             *  - some host bridges are disabled
>>>>>> +             * Make sure we insert the correct "linux,pci-domain" 
>>>>>> property
>>>>>> +             * in any case, so we know which segments will be used
>>>>>> +             * by Linux for which bridges.
>>>>>
>>>>> The check above will check the node type is "pci". AFAICT, this would 
>>>>> also cover PCI devices. I am not aware of any issue to add 
>>>>> "linux,pci-domain" for them. However, this feels a bit odd.
>>>>>
>>>>>   From my understanding, a PCI device would always be described as a 
>>>>> child of the hostbridges. So I would rework the 'if' to also check if the 
>>>>> parent type is not "pci".
>>>>>
>>>> We may have "bridge -> bridge -> device" topology as well.
>>>
>>> Do you have an example of Device-Tree?
>> No, I don't have at hand, but I can imagine this can relatively easy be done 
>> with QEMU > Even if not, do you assume this topology can never happen?
>
> I think it is not possible to describe them in the Device-Tree because you 
> wouldn't be able to translate the "regs" of the nested hostbridge to an 
> actual MMIO address.
>
> In fact, looking at dt_device_get_address(), I think Xen would reject such DT.
>
>>>
>>>> So, I prefer to have the check as it is.
>>>
>>> I don't really like the idea to spuriously add "linux,pci-domain" to PCI DT 
>>> node. But if there are no other solution, then this should at least be 
>>> mentionned in the commit message and code.
>> I am fine with any solution here, I just want that to be defined and 
>> implemented.
>> Please let me know the final decision on this and how we proceed
>
> I would prefer to go with my way. This can be refined in the future if we 
> find Device-Tree that matches what you wrote.
Ok, so just to make it clear:
 >a PCI device would always be described as a child of the hostbridges. So I 
 >would rework the 'if' to also check if the parent type is not "pci"
>
> Cheers,
>
Thank you,
Oleksandr