linux-kernel - Re: [RFC 04/20] iommu: Add iommu_device_get

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Message-ID: <20210922050746.GA12921@lst.de>
Date:   Wed, 22 Sep 2021 07:07:46 +0200
From:   Christoph Hellwig <hch@....de>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>, Liu Yi L <yi.l.liu@...el.com>,
        alex.williamson@...hat.com, hch@....de, jasowang@...hat.com,
        joro@...tes.org, jean-philippe@...aro.org, kevin.tian@...el.com,
        parav@...lanox.com, lkml@...ux.net, pbonzini@...hat.com,
        lushenming@...wei.com, eric.auger@...hat.com, corbet@....net,
        ashok.raj@...el.com, yi.l.liu@...ux.intel.com,
        jun.j.tian@...el.com, hao.wu@...el.com, dave.jiang@...el.com,
        jacob.jun.pan@...ux.intel.com, kwankhede@...dia.com,
        robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, david@...son.dropbear.id.au,
        nicolinc@...dia.com
Subject: Re: [RFC 04/20] iommu: Add iommu_device_get_info interface

On Wed, Sep 22, 2021 at 10:31:47AM +0800, Lu Baolu wrote:
> Hi Jason,
>
> On 9/22/21 12:19 AM, Jason Gunthorpe wrote:
>> On Sun, Sep 19, 2021 at 02:38:32PM +0800, Liu Yi L wrote:
>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>>
>>> This provides an interface for upper layers to get the per-device iommu
>>> attributes.
>>>
>>>      int iommu_device_get_info(struct device *dev,
>>>                                enum iommu_devattr attr, void *data);
>>
>> Can't we use properly typed ops and functions here instead of a void
>> *data?
>>
>> get_snoop()
>> get_page_size()
>> get_addr_width()
>
> Yeah! Above are more friendly to the upper layer callers.

The other option would be a struct with all the attributes.  Still
type safe, but not as many methods.  It'll require a little boilerplate
in the callers, though.