netdev - RE: [PATCH RFC] pci: Control whether VFs are probed on pci_enable

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Message-ID: <B5657A6538887040AD3A81F1008BEC63BA78ED@avmb3.qlogic.org>
Date:	Tue, 9 Dec 2014 07:07:27 +0000
From:	Yuval Mintz <Yuval.Mintz@...gic.com>
To:	Eli Cohen <eli@....mellanox.co.il>
CC:	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	David Miller <davem@...emloft.net>,
	linux-pci <linux-pci@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	"ogerlitz@...lanox.com" <ogerlitz@...lanox.com>,
	"yevgenyp@...lanox.com" <yevgenyp@...lanox.com>,
	Donald Dutile <ddutile@...hat.com>
Subject: RE: [PATCH RFC] pci: Control whether VFs are probed on
 pci_enable_sriov

> > >Currently the kerenl will call probe for any device for which there
> > >is a supporting driver and I did not want to change that.
> >
> > But what's next? How will this feature be activated?
> >
> > Adding a parameter to pci_enable_sriov() might give developers the
> > false impression they can change behavior by passing `0' to this
> > function; But that shouldn't be the method to control this - we should
> > have uniform control of the feature across different drivers, e.g., by an
> additional sysfs node.
> 
> I was planning on using this on mlx5 SRIOV support which is not available
> upstream yet. So this could be a driver developer's decision how to use this.

I think it shouldn't - from user perspective, you can't have such fundamental
difference between different drivers - that enabling sriov on one device would
create VFs in the hypervisors and another one won't.

> I think adding another sysfs entry to control this behavior is unnecessary since the
> administrator has the freedom to later do any bidnings he wishes to do.
> 
> Keeping things as they are today is not so "nice". I mean, I could fail probe for
> VFs to avoid them from being initialized at the hypervisor but there are other
> questions: which error should I return and how can I be sure how the bus driver
> will refer to such failures.

Again - you could say that this is solely in your drivers decision-making-area,
but failing the VF probe would lead to the same difference between drivers I've
stated before.

> So, maybe the solution I suggested is not the best one but do we agree that this
> needs to be addressed this way or another?

All-in-all, I agree. But I think the solution should be user-controlled and not driver-based.
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