Re: [PATCH 1/4] iommu/vt-d: Introduce dev_to_iommu()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Nov 16, 2023 at 11:23:56AM +0800, Baolu Lu wrote:
> On 11/16/23 11:19 AM, Tian, Kevin wrote:
> > > From: Lu Baolu <baolu.lu@linux.intel.com>
> > > Sent: Thursday, November 16, 2023 9:51 AM
> > > 
> > > +static inline struct intel_iommu *dev_to_iommu(struct device *dev)
> > > +{
> > > +	/*
> > > +	 * Assume that valid per-device iommu structure must be installed
> > > +	 * if iommu_probe_device() has succeeded. This helper could only
> > > +	 * be used after device is probed.
> > > +	 */
> > > +	return ((struct device_domain_info *)dev_iommu_priv_get(dev))-
> > > > iommu;
> > > +}
> > 
> > Not sure whether this helper is useful. This is only used by 2 out of 5
> > post-probe users. Probably just open-coding in all 5 places is clearer.
> 
> I thought it should get more users in the future development.

The pattern in the SMMUv2 driver is like

  struct device_domain_info *info = dev_iommu_priv_get(dev);
  struct intel_iommu *iommu = info->iommu;

Which really isn't worth the helper, unless you have lots of caes
where info isn't needed at all?

Jason