linux-kernel - Re: [Patch V1 0/6] Refine generic/PCI MSI irqodmian interfaces

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Message-ID: <5466259A.7060505@linux.intel.com>
Date:	Fri, 14 Nov 2014 23:54:02 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Yijing Wang <wangyijing@...wei.com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Tony Luck <tony.luck@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Patch V1 0/6] Refine generic/PCI MSI irqodmian interfaces

On 2014/11/14 5:28, Marc Zyngier wrote:
> On 13/11/14 21:11, Thomas Gleixner wrote:
>> On Thu, 13 Nov 2014, Marc Zyngier wrote:
>>> With the new stacked irq domains, it becomes pretty tempting
>>> to allocate an MSI domain per PCI bus, which would remove
>>> the requirement of either relying on arch-specific code, or
>>> a default PCI MSI domain.
>>
>> Right. That's what I roughly had in mind. And that would solve the
>> multi-iommu issue on x86 nicely as well. We establish the association
>> at the time where the bus gets populated. So the whole lookup magic
>> simply goes away.
> 
> Great. I've pushed the whole thing out with this patch, the couple
> of fixes I mentioned earlier, as well as the whole ITS code:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git irq/stacked-its-v2
Hi Marc,
	I have looked at the code, and found some issues.
1) With my next version, no need to implemeent its_pci_msi_free()
anymore. msi_domain_free_irqs() will reset desc->irq to zero
for all architectures.

2) This piece of code in its_msi_prepare() may run into trouble
for PCI device with both MSI and MSIX capability. I will change
msi_prepare() prototype to pass in the "nvec" parameter. And you
may access first_pci_msi_entry()->msi_attrib.is_msix to get
allocation type if needed.
	nvec = pci_msix_vec_count(pdev);
	if (nvec < 0)
		nvec = pci_msi_vec_count(pdev);
	if (nvec < 0)
		return nvec;

3) Do we need to increase the default of NUM_MSI_ALLOC_SCRATCHPAD_REGS
to 4? 2 is a little too limited.

Regards!
Gerry

> 
> Time to go home.
> 
> 	M.
> 
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