Re: [PATCH v12 14/21] powerpc/powernv: Allocate struct pnv_ioda_pe iommu_table dynamically

[Bjorn Helgaas <bhelgaas@google.com>]

On Mon, Mar 02, 2015 at 03:50:37PM +0800, Wei Yang wrote:
> On Tue, Feb 24, 2015 at 02:46:53AM -0600, Bjorn Helgaas wrote:
> >On Tue, Feb 24, 2015 at 02:34:35AM -0600, Bjorn Helgaas wrote:
> >> From: Wei Yang <weiyang@linux.vnet.ibm.com>
> >> 
> >> Current iommu_table of a PE is a static field.  This will have a problem
> >> when iommu_free_table() is called.
> >> 
> >> Allocate iommu_table dynamically.
> >
> >I'd like a little more explanation about why we're calling
> >iommu_free_table() now when we didn't call it before.  Maybe this happens
> >when we disable SR-IOV and the VFs go away?
> 
> Yes, it is called in disable path.
> 
> pcibios_sriov_disable
>     pnv_pci_sriov_disable
>         pnv_ioda_release_vf_PE
> 	    pnv_pci_ioda2_release_dma_pe
> 	        iommu_free_table            <--- here it is invoked
> 
> 
> >
> >Is there a hotplug remove path where we should also be calling
> >iommu_free_table()?
> 
> When VF is not introduced, no one calls this on powernv platform.
> 
> Each PCI bus is a PE and it has its own iommu table, even a device is
> hotpluged, the iommu table will not be released.

None of this explanation made it into the v13 patch.  And I don't quite
understand it anyway.

Something like "Previously the iommu_table had the same lifetime as a
struct pnv_ioda_pe and was embedded in it.  The pnv_ioda_pe was allocated
when XXX and freed when YYY.  This no longer works: we can't allocate the
iommu_table at the same time as the pnv_ioda_pe because XXX, so we allocate
it when XXX and free it when YYY."

Bjorn