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

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Date:   Sat, 18 Nov 2023 10:26:58 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com, "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 11/17/23 9:07 PM, Jason Gunthorpe wrote:
> 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?

No. As Kevin pointed out, there are only 2 places.

I will drop this helper.

Best regards,
baolu