linux-kernel - Re: [Patch Part2 v4 20/31] PCI/MSI: Kill redundant calling for irq_set_msi

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Message-ID: <545ACFC7.9090204@huawei.com>
Date:	Thu, 6 Nov 2014 09:32:55 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Grant Likely <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	"Matthias Brugger" <matthias.bgg@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Tony Luck" <tony.luck@...el.com>, Joerg Roedel <joro@...tes.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Patch Part2 v4 20/31] PCI/MSI: Kill redundant calling for irq_set_msi_desc()
 for MSIx interrupts

On 2014/11/6 6:45, Bjorn Helgaas wrote:
> On Tue, Nov 04, 2014 at 08:01:54PM +0800, Jiang Liu wrote:
>> It's arch_setup_msi_irq()/arch_setup_msi_irqs()'s responsibility to call
>> irq_set_msi_desc() to associate IRQ descriptors and MSI descriptors,
>> so kill the redundant call of irq_set_msi_desc() for MSIx interrupts
>> in PCI MSI core.
> 
> "MSI-X" in English text, "msix" in code.
> 
> The default arch_setup_msi_irq() in drivers/pci/msi.c doesn't call
> irq_set_msi_desc().  Does it happen somewhere inside chip->setup_irq()?

Yes.

I also found this.
http://www.spinics.net/lists/linux-pci/msg34256.html

> 
> I don't know how to verify that there are calls in all the places needed.
> That makes me wonder if the factoring is wrong -- maybe irq_set_msi_desc()
> could be done in some common place.

In my idea, place the irq_set_msi_desc() in common MSI core is ok, but currently almost
all MSI arch code call irq_set_msi_desc() in arch code. So a lot of code need to change.
And arch code setup MSI and MSI-X in the same way, so if MSI work happy without irq_set_msi_desc(entry->irq, entry)
in common MSI code, MSI-X should be the same.

> 
>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
>> ---
>>  drivers/pci/msi.c |    1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index afe974600c7d..da181c59394b 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -685,7 +685,6 @@ static void msix_program_entries(struct pci_dev *dev,
>>  						PCI_MSIX_ENTRY_VECTOR_CTRL;
>>  
>>  		entries[i].vector = entry->irq;
>> -		irq_set_msi_desc(entry->irq, entry);
>>  		entry->masked = readl(entry->mask_base + offset);
>>  		msix_mask_irq(entry, 1);
>>  		i++;
>> -- 
>> 1.7.10.4
>>
> --
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> 
> .
> 


-- 
Thanks!
Yijing

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