linux-kernel - Re: [PATCH v2 2/8] PCI/MSI: Add hooks to populate the msi

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Date:	Wed, 14 Jan 2015 10:04:14 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>
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>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>
Subject: Re: [PATCH v2 2/8] PCI/MSI: Add hooks to populate the msi_domain
 field

>>> +static void pci_set_msi_domain(struct pci_dev *dev)
>>> +{
>>> +	/*
>>> +	 * If no domain has been set through the pcibios callback,
>>> +	 * inherit the default from the bus device.
>>> +	 */
>>> +	if (!dev_get_msi_domain(&dev->dev))
>>> +		dev_set_msi_domain(&dev->dev,
>>> +				   dev_get_msi_domain(&dev->bus->dev));
>>> +}
>>
>> Hi Marc, now we have two ways to associate the pci_dev and msi_domain, right ?
>>
>> 1. associate pci_dev and msi_domain in pcibios_add_device() like x86.
>>
>> 2. Inherit msi_domain from pci_dev->bus.
>>
>> My question is if all pci devices inherit msi_domain from the pci_bus,
>> so all pci devices under same pci host bridge have the same msi_domain assigned by
>> weak pcibios_set_phb_msi_domain(). So why not save the pci host bridge specific
>> msi_domain in pci_host_bridge. Then pci devices could inherit the msi_domain from
>> its pci host bridge directly, no need to involve pci bus in the assignment.
> 
> But then, you would end-up maintaining another msi_domain field inside
> the pci_host bridge structure. What do you gain by doing so?

My original thought is holding msi_domain field inside the pci_host_bridge is
more simple than every bus maintaining the msi_domain, but this proposal has a
disadvantage that sometimes we must setup for every device. I checked x86 DMAR code,
and found most DMAR would report PCIe root port device associating the msi_domain, not the EP device.
So pcibios_add_device could only associate these bridge device msi_domain, and its children
devices will propagate from their parent bus(get msi_domain from its bridge).

So now I agree your idea, please forgive my nagging :)

Thanks!
Yijing.

> 
> With this series, msi_domain has the nice property of always being tied
> to a device (and struct pci_bus always has a device). We always have
> phb->bus->dev.msi_domain within reach, and architecture code can decide
> to override it on a per-device basis.
> 
> What else do you need? What am I missing from your proposal?
> 
> Thanks,
> 
> 	M.
> 


-- 
Thanks!
Yijing

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