linux-kernel - Re: [PATCH] iommu/amd - Use dev_err to send events to the system log

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Date:   Wed, 14 Feb 2018 12:49:57 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     "Hook, Gary" <ghook@....com>
Cc:     Gary R Hook <gary.hook@....com>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd - Use dev_err to send events to the system log

On Tue, Feb 13, 2018 at 02:24:56PM -0500, Hook, Gary wrote:
> Without actually running a driver and getting some debug info, I'll just
> say that my example compiled, the amd_iommu structure points to a pci_dev
> which contains a device, and the two possibilities are likely equivalent.
> 
> I'll vet that, of course, but working under the assumption that they are
> equivalent, the question becomes, do you have a preference?

They are not equivalent, your version points to the pci_dev containing
the IOMMU, my version points to the (virtual) iommu-device for that
particular iommu in the kernel.

So the difference in the prefix is:

	your version: '0000:00:00.2:'

	vs. my version: 'ivhd0:'

The latter is the better prefix, because it points to the iommu. A
pci_dev can contain more than one iommu, so that prefix is not specific
enough. I know that there is currently no hardware implementing multiple
iommus on one pci_dev, but it is allowed according to the spec.

Regards,

	Joerg