Subject: [PATCH 2/6] PCI/MSI: add hooks to populate the msi_domain field

From: [email-masked] (Jiang Liu)
Date: Tue, 09 Dec 2014 23:42:02 +0800

On 2014/12/9 22:59, Marc Zyngier wrote:
> On 09/12/14 14:35, Jiang Liu wrote:
>> On 2014/12/9 22:27, Marc Zyngier wrote:
>>> On 09/12/14 14:11, Jiang Liu wrote:
>>>> On 2014/12/9 22:03, Marc Zyngier wrote:
>>>>> Hi Gerry,
>>>>>
>>>>> On 09/12/14 12:47, Jiang Liu wrote:
>>>>>> On 2014/12/9 20:12, Marc Zyngier wrote:
>>>>>>> Yijing,
>>>>>>>
>>>>>>> On 09/12/14 11:57, Yijing Wang wrote:
>>>>>>>>>>> +void __weak pcibios_set_phb_msi_domain(struct pci_bus *bus)
>>>>>>>>>>> +{
>>>>>>>>>>> +}
>>>>>>>>>>> +
>>>>>>>>>>> +static void pci_set_bus_msi_domain(struct pci_bus *bus)
>>>>>>>>>>> +{
>>>>>>>>>>> +	struct pci_dev *bridge = bus->self;
>>>>>>>>>>> +
>>>>>>>>>>> +	if (!bridge)
>>>>>>>>>>> +		pcibios_set_phb_msi_domain(bus);
>>>>>>>>>>> +	else
>>>>>>>>>>> +		dev_set_msi_domain(&bus->dev, dev_get_msi_domain(&bridge->dev));
>>>>>>>>>>> +}
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Hi Marc, we can not assume pci devices under same phb share the same msi irq domain,
>>>>>>>>>> now in x86, pci devices under the same phb may associate different msi irq domain.
>>>>>>>>
>>>>>>>> Hi Marc,
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Well, this is not supposed to be a perfect solution yet, but instead a
>>>>>>>>> basis for discussion. What I'd like to find out is:
>>>>>>>>>
>>>>>>>>> - What is the minimum granularity for associating a device with its MSI
>>>>>>>>> domain in existing platforms?
>>>>>>>>
>>>>>>>> PCI device, after Gerry's msi irq domain patchset which now in linux-next,
>>>>>>>> in x86, we will find msi irq domain by pci_dev.
>>>>>>>
>>>>>>> Are you *really* associating the MSI domain on a per pci-device basis?
>>>>>>> That is, you have devices on the same PCI bus talking to different MSI hw?
>>>>>> Hi Marc,
>>>>>> 	This is a little wild:(
>>>>>> 	On x86 platform with Intel VT-d(not the case for AMD-v),
>>>>>> interrupt remapping is tight to DMA remapping (IOMMU) unit.
>>>>>> For most common cases, IOMMU unit manages PCI bus and its sub-hierarchy.
>>>>>> But it may also manage a specific PCI device. This is typically used to
>>>>>> provide QoS for audio device by using dedicated IOMMU unit to avoid
>>>>>> resource contention on DMA remapping tables. BIOS uses ACPI table to
>>>>>> report PCI bus/device to IOMMU unit mapping relationship. (To be honest,
>>>>>> I have no really experience with such a hardware platform yet, just for
>>>>>> theoretical analysis)
>>>>>> 	On the other hand, we now support hierarchy irqdomain. So to
>>>>>> support per-PCI IOMMU unit case, we need maintain irqdomain at PCI
>>>>>> device level.
>>>>>> 	This piece of code from your [4/6] is flexible enough, which
>>>>>> retrieves msi_domain from PCI device, then fallback to PCI bus,
>>>>>> then fallback to platform specific method.
>>>>>> 	domain = dev_get_msi_domain(&dev->dev);
>>>>>> 	if (!domain && dev->bus->msi)
>>>>>>  		domain = dev->bus->msi->domain;
>>>>>>  	if (!domain)
>>>>>>  		domain = arch_get_pci_msi_domain(dev);
>>>>>
>>>>> OK. But what I'd really like to see is a way to setup the
>>>>> device<->domain binding as early as possible, without having to use more
>>>>> conditional code in pci_msi_get_domain.
>>>>>
>>>>> IOW, can we do something similar to what pci_set_bus_msi_domain and
>>>>> pci_set_msi_domain do in this patch?
>>>> Hi Marc,
>>>> 	I have checked x86 code, we could set pci_dev->msi_domain
>>>> when creating PCI devices, just need to find some hook points
>>>> into PCI core next step. If arch code doesn't set pci_dev->msi_domain,
>>>> PCI MSI core may provide a default way to set pci_dev->msi_domain.
>>>> This may make the implementation simpler, I guess:)
>>>
>>> Right. So following your earlier suggestion, I could make
>>> pci_set_msi_domain a weak symbol and let arch code override this.
>>>
>>> My preference would have been to have arch code to create a set of
>>> arch-independent data structures describing the topology, and use that
>>> for everything, but maybe that's a bit ambitious for a start.
>>>
>>> I'll rework the series to make the symbols weak.
>> Hi Marc,
>> 	I think we may not need the weak symbol at all. With following
>> draft patch, the PCI MSI core may simply do:
>> 	if (pci_dev->dev.msi_domain == NULL)
>> 		dev_set_msi_domain(&dev->dev,
>> 			 dev_get_msi_domain(&dev->bus->dev));
>> -----------------------------------------------------------------------
>> Note: the patch won't pass compilation, just to show the key idea:)
>>
>> diff --git a/arch/x86/kernel/apic/msi.c b/arch/x86/kernel/apic/msi.c
>> index da163da5fdee..8147d25d4349 100644
>> --- a/arch/x86/kernel/apic/msi.c
>> +++ b/arch/x86/kernel/apic/msi.c
>> @@ -67,6 +67,23 @@ static struct irq_chip pci_msi_controller = {
>>         .flags                  = IRQCHIP_SKIP_SET_WAKE,
>>  };
>>
>> +struct irq_domain *x86_get_pci_msi_domain(struct pci_dev *dev)
>> +{
>> +       struct irq_domain *domain;
>> +       struct irq_alloc_info info;
>> +
>> +       init_irq_alloc_info(&info, NULL);
>> +       info.type = X86_IRQ_ALLOC_TYPE_MSI;
>> +       info.msi_dev = dev;
>> +       domain = irq_remapping_get_irq_domain(&info);
>> +       if (domain == NULL)
>> +               domain = msi_default_domain;
>> +       if (domain == NULL)
>> +               domain = ERR_PTR(-ENOSYS);
>> +
>> +       return domain;
>> +}
>> +
>>  int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
>>  {
>>         struct irq_domain *domain;
>> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
>> index 7b20bccf3648..a26f30a8bb8f 100644
>> --- a/arch/x86/pci/common.c
>> +++ b/arch/x86/pci/common.c
>> @@ -652,6 +652,9 @@ int pcibios_add_device(struct pci_dev *dev)
>>                 pa_data = data->next;
>>                 iounmap(data);
>>         }
>> +
>> +       dev->dev.msi_domain = x86_get_pci_msi_domain(dev);
>> +
>>         return 0;
>>  }
> 
> Right. So you set the msi_domain using the pcibios_add_device callback.
> That will require some minimal surgery (the call to pci_set_msi_domain
> happens before the pcibios call, so it needs to be relocated after), but
> that seems like a sensible solution to me.
So the key point is clear now:
The PCI MSI core will try to set a default value for
pci_dev->dev.msi_domain if the arch code doesn't do that.

Seems like a solution:)

> Thanks!
> 	M.