linux-kernel - Re: [RFC PATCH 0/2] iommu/s390: Fix iommu-groups and add sysfs support

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Date:   Fri, 28 Apr 2017 17:25:20 +0200 (CEST)
From:   Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:     Joerg Roedel <joro@...tes.org>
cc:     Gerald Schaefer <gerald.schaefer@...ibm.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] iommu/s390: Fix iommu-groups and add sysfs
 support

On Fri, 28 Apr 2017, Joerg Roedel wrote:
> On Fri, Apr 28, 2017 at 02:46:34PM +0200, Gerald Schaefer wrote:
> > On Thu, 27 Apr 2017 23:03:25 +0200
> > Joerg Roedel <joro@...tes.org> wrote:
> > 
> > > > Well, there is a separate zpci_dev for each pci_dev on s390,
> > > > and each of those has its own separate dma-table (thus not shared).  
> > > 
> > > Is that true for all functions of a PCIe card, so does every function of
> > > a device has its own zpci_dev structure and thus its own DMA-table?
> > 
> > Yes, clp_add_pci_device() is called for every function, which in turn calls
> > zpci_create_device() with a freshly allocated zdev. zpci_enable_device()
> > then sets up a new DMA address space for each function.
> 
> That sounds special :) So will every function of a single device end up
> as a seperate device on a seperate root-bus?

Yes. That's true even for multi-function and SRIOV.

> > > My assumption came from the fact that the zpci_dev is read from
> > > pci_dev->sysdata, which is propagated there from the pci_bridge
> > > through the pci_root_bus structures.
> > 
> > The zdev gets there via zpci_create_device() -> zpci_scan_bus() ->
> > pci_scan_root_bus(), which is done for every single function.
> > 
> > Not sure if I understand this right, but it looks like we set up a new PCI
> > bus for each function.
> 
> Yeah, it sounds like this. Maybe Sebastian can confirm that?

Yes. Confirmed.

Regards,
Sebastian