Re: [PATCH 1/5] iommu: Implement iommu_put_resv_regions_simple()

[Thierry Reding <thierry.reding@gmail.com>]

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On Wed, Sep 18, 2019 at 04:37:38PM +0100, Will Deacon wrote:
> On Thu, Aug 29, 2019 at 01:17:48PM +0200, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > Implement a generic function for removing reserved regions. This can be
> > used by drivers that don't do anything fancy with these regions other
> > than allocating memory for them.
> > 
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> >  drivers/iommu/iommu.c | 19 +++++++++++++++++++
> >  include/linux/iommu.h |  2 ++
> >  2 files changed, 21 insertions(+)
> > 
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 0f585b614657..73a2a6b13507 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -2170,6 +2170,25 @@ void iommu_put_resv_regions(struct device *dev, struct list_head *list)
> >  		ops->put_resv_regions(dev, list);
> >  }
> >  
> > +/**
> > + * iommu_put_resv_regions_simple - Reserved region driver helper
> > + * @dev: device for which to free reserved regions
> > + * @list: reserved region list for device
> > + *
> > + * IOMMU drivers can use this to implement their .put_resv_regions() callback
> > + * for simple reservations. Memory allocated for each reserved region will be
> > + * freed. If an IOMMU driver allocates additional resources per region, it is
> > + * going to have to implement a custom callback.
> > + */
> > +void iommu_put_resv_regions_simple(struct device *dev, struct list_head *list)
> > +{
> > +	struct iommu_resv_region *entry, *next;
> > +
> > +	list_for_each_entry_safe(entry, next, list, list)
> > +		kfree(entry);
> > +}
> > +EXPORT_SYMBOL(iommu_put_resv_regions_simple);
> 
> Can you call this directly from iommu_put_resv_regions() if the function
> pointer in ops is NULL? That would save having to plumb the default callback
> into a bunch of drivers.

I probably could, but I don't think that necessarily improves things.
The reason is that that would cause the helper to get called even if the
driver doesn't support reserved regions. That's likely harmless because
in that case the list of regions passed to it would be empty. However, I
think the current way to do this, where we have to implement both hooks
for ->get_resv_regions() and ->put_resv_regions() is nicely symmetric.

Thierry

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