linux-kernel - Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X

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Message-ID: <560DDC0F.80302@gmail.com>
Date:	Thu, 1 Oct 2015 18:21:19 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	hjk@...sjkoch.de, gregkh@...ux-foundation.org, dev@...k.org,
	linux-kernel@...r.kernel.org
Subject: Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X

On 10/01/2015 05:01 PM, Stephen Hemminger wrote:
> On Thu, 1 Oct 2015 16:40:10 -0700
> Alexander Duyck <alexander.duyck@...il.com> wrote:
>
>> I agree with some other reviewers.  Why call pci_enable_msix in open?
>> It seems like it would make much more sense to do this on probe, and
>> then disable MSI-X on free.  I can only assume you are trying to do it
>> to save on resources but the fact is this is a driver you have to
>> explicitly force onto a device so you would probably be safe to assume
>> that they plan to use it in the near future.
> Because if interface is not up, the MSI handle doesn't have to be open.
> This saves resources and avoids some races.

Yes, but it makes things a bit messier for the interrupts.  Most drivers 
take care of interrupts during probe so that if there are any allocation 
problems they can take care of them then instead of leaving an interface 
out that will later fail when it is brought up.  It ends up being a way 
to deal with the whole MSI-X fall-back issue.

- Alex
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