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

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Date:	Tue, 09 Dec 2014 14:27:53 +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

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.

Thanks,

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