linux-kernel - Re: [PATCH 2/6] PCI/MSI: add hooks to populate the msi

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Date:	Tue, 09 Dec 2014 14:03:23 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Yijing Wang <wangyijing@...wei.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>
Subject: Re: [PATCH 2/6] PCI/MSI: add hooks to populate the msi_domain field

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?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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