Re: [PATCH 1/2] irqdomain: add empty irq_domain_check_msi_remap

[Mian Yousaf Kaukab]

On 03/02/2017 02:12 PM, Auger Eric wrote:
> Hi Yousaf,
>
> On 02/03/2017 13:23, Mian Yousaf Kaukab wrote:
> > On 03/02/2017 11:24 AM, Auger Eric wrote:
> > > Hi Mian Yousaf,
> > >
> > > On 02/03/2017 11:01, Mian Yousaf Kaukab wrote:
> > > > Fix following build error for s390:
> > > > drivers/vfio/vfio_iommu_type1.c: In function
> > > > 'vfio_iommu_type1_attach_group':
> > > > drivers/vfio/vfio_iommu_type1.c:1290:25: error: implicit declaration
> > > > of function 'irq_domain_check_msi_remap'
> > > >
> > > > Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@xxxxxxxx>
> > > > ---
> > > >    include/linux/irqdomain.h | 4 ++++
> > > >    1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
> > > > index 188eced6813e..137817b08cdc 100644
> > > > --- a/include/linux/irqdomain.h
> > > > +++ b/include/linux/irqdomain.h
> > > > @@ -524,6 +524,10 @@ static inline struct irq_domain
> > > > *irq_find_matching_fwnode(
> > > >    {
> > > >        return NULL;
> > > >    }
> > > > +static inline bool irq_domain_check_msi_remap(void)
> > > > +{
> > > > +    return true;
> > > By default you should rather return false, reporting there is no MSI
> > > remapping capability on irq domain side. Besides thank you for the fix.
> > I choose to return true based on the function header comments of
> > irq_domain_check_msi_remap. It says
> >
> > "Return: false if any MSI irq domain does not support IRQ remapping,
> > true otherwise (including if there is no MSI irq domain)"
> >
> > So function should return true in case of no MSI irq domain. Have I miss
> > understood this?
> This behavior is indeed mandated on ARM - where MSI are translated by
> the smmu - to allow safe device assignment if there is no MSI domain,
> ie. in this situation there is no risk an assigned device writes into an
> MSI doorbell.
>
> As the function is not implemented at all in your case, personally I
> would rather be defensive though and return false. You were not able to
> check the capability.
OK Agree. I will send an update as soon as a decision is made on 2/2.

BR,
Yousaf