netdev - Re: [PATCH net-next] cxgb4: Fix for SR-IOV VF initialization

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Message-ID: <53CF2570.50103@gmail.com>
Date:	Tue, 22 Jul 2014 20:01:04 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	David Miller <davem@...emloft.net>, hariprasad@...lsio.com
CC:	netdev@...r.kernel.org, leedom@...lsio.com, nirranjan@...lsio.com,
	kumaras@...lsio.com, anish@...lsio.com
Subject: Re: [PATCH net-next] cxgb4: Fix for SR-IOV VF initialization

On 07/22/2014 03:34 PM, David Miller wrote:
> From: Hariprasad Shenai <hariprasad@...lsio.com>
> Date: Tue, 22 Jul 2014 16:26:20 +0530
> 
>> Commit 35b1de5 ("rdma/cxgb4: Fixes cxgb4 probe failure in VM when PF is exposed
>> through PCI Passthrough") introduced a regression, where VF failed to
>> initialize. This commit fixes it.
>>
>> Signed-off-by: Casey Leedom <leedom@...lsio.com>
>> Signed-off-by: Hariprasad Shenai <hariprasad@...lsio.com>
> 
> This commit message need to explain things better, how exactly was
> the regression introduced, what's exactly wrong with the current code?
> 
> I actually can't figure it out myself, other than to say that maybe
> replacing things with:
> 
> 	func = PCI_FUNC(pdev->devfn);
>  	if (func < ARRAY_SIZE(num_vf) && num_vf[func] > 0)
>  		if (pci_enable_sriov(pdev, num_vf[func]) == 0)
> 
> would work equally as well.  That's precisely what the code was
> doing before the mentioned commit.
> 
> Why do we have to iterate over _ALL_ functions of the PCI device,
> rather than just directly enable SRIOV on the one function whether
> it bet PCI_FUNC(pdev->devfn) or that WHOAMI value?
> 
> You need to explain this so that people understand the how and the
> why of your changes.
> 
> Thanks.

What it looks like it is doing is forcing the loop to iterate over
multiple PFs enabling SR-IOV on each one.  Same thing for disabling on
remove.  I would think this would fail for a multifunction device since
calling this a pci_enable_sriov a second time with values when SR-IOV is
enabled should return -EINVAL.

I thought the use of module parameters for SR-IOV had been deprecated in
favor of the PCI sysfs approach?  It seems like switching over might be
a better way to resolve whatever issue this was trying to address.

Thanks,

Alex




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