linux-kernel - Re: [PATCH 1/4] iommu/vt-d: Introduce dev_to

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Message-ID: <20231117130756.GA6501@ziepe.ca>
Date:   Fri, 17 Nov 2023 09:07:56 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] iommu/vt-d: Introduce dev_to_iommu()

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@...ux.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