netdev - Re: [PATCH v2 net-next 2/2] ionic: support sr-iov operations

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Date:   Thu, 12 Dec 2019 22:24:45 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Shannon Nelson <snelson@...sando.io>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH v2 net-next 2/2] ionic: support sr-iov operations

On 12/12/2019 3:35 PM, Jakub Kicinski wrote:
> On Thu, 12 Dec 2019 11:59:50 -0800, Shannon Nelson wrote:
>> On 12/12/19 11:52 AM, Jakub Kicinski wrote:
>>> On Thu, 12 Dec 2019 06:53:42 +0000, Parav Pandit wrote:  
>>>>>   static void ionic_remove(struct pci_dev *pdev)
>>>>>   {
>>>>>   	struct ionic *ionic = pci_get_drvdata(pdev);
>>>>> @@ -257,6 +338,9 @@ static void ionic_remove(struct pci_dev *pdev)
>>>>>   	if (!ionic)
>>>>>   		return;
>>>>>   
>>>>> +	if (pci_num_vf(pdev))
>>>>> +		ionic_sriov_configure(pdev, 0);
>>>>> +  
>>>> Usually sriov is left enabled while removing PF.
>>>> It is not the role of the pci PF removal to disable it sriov.  
>>> I don't think that's true. I consider igb and ixgbe to set the standard
>>> for legacy SR-IOV handling since they were one of the first (the first?)
>>> and Alex Duyck wrote them.
>>>
>>> mlx4, bnxt and nfp all disable SR-IOV on remove.  
>>
>> This was my understanding as well, but now I can see that ixgbe and i40e 
>> are both checking for existing VFs in probe and setting up to use them, 
>> as well as the newer ice driver.  I found this today by looking for 
>> where they use pci_num_vf().
> 
> Right, if the VFs very already enabled on probe they are set up.
> 
> It's a bit of a asymmetric design, in case some other driver left
> SR-IOV on, I guess.
> 

I remember on one email thread on netdev list from someone that in one
use case, they upgrade the PF driver while VFs are still bound and
SR-IOV kept enabled.
I am not sure how much it is used in practice/or practical.
Such use case may be the reason to keep SR-IOV enabled.