Re: [PATCH 1/7] genirq/msi: Add a new field in msi_desc to store an IOMMU cookie

[Julien Grall]

On 4/23/19 11:23 AM, Marc Zyngier wrote:
> Hi Julien,

Hi Marc,

> On 18/04/2019 18:26, Julien Grall wrote:
> > When an MSI doorbell is located downstream of an IOMMU, it is required
> > to swizzle the physical address with an appropriately-mapped IOVA for any
> > device attached to one of our DMA ops domain.
> >
> > At the moment, the allocation of the mapping may be done when composing
> > the message. However, the composing may be done in non-preemtible
> > context while the allocation requires to be called from preemptible
> > context.
> >
> > A follow-up patch will split the current logic in two functions
> > requiring to keep an IOMMU cookie per MSI.
> >
> > This patch introduces a new field in msi_desc to store an IOMMU cookie
> > when CONFIG_IOMMU_DMA is selected.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> > ---
> >   include/linux/msi.h | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/include/linux/msi.h b/include/linux/msi.h
> > index 7e9b81c3b50d..d7907feef1bb 100644
> > --- a/include/linux/msi.h
> > +++ b/include/linux/msi.h
> > @@ -77,6 +77,9 @@ struct msi_desc {
> >   	struct device			*dev;
> >   	struct msi_msg			msg;
> >   	struct irq_affinity_desc	*affinity;
> > +#ifdef CONFIG_IOMMU_DMA
> > +	const void			*iommu_cookie;
> > +#endif
> >   
> >   	union {
> >   		/* PCI MSI/X specific data */
>
> Given that this is the only member in this structure that is dependent
> on a config option, you could also add a couple of accessors that would
> do nothing when IOMMU_DMA is not selected (and use that in the DMA code).

I haven't seen any use of the helpers so far because the DMA code is 
also protected by IOMMU_DMA.

I can add the helpers in the next version if you see any use outside of 
the DMA code.

Cheers,

--
Julien Grall