linux-kernel - Re: [PATCH 7/7] iommu: Add iommu_domain::domain

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Date:   Tue, 25 Jan 2022 12:42:50 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] iommu: Add iommu_domain::domain_ops

On 1/24/22 5:37 PM, Christoph Hellwig wrote:
> On Mon, Jan 24, 2022 at 03:11:02PM +0800, Lu Baolu wrote:
>> Add a domain specific callback set, domain_ops, for vendor iommu driver
>> to provide domain specific operations. Move domain-specific callbacks
>> from iommu_ops to the domain_ops and hook them when a domain is allocated.
> 
> Ah, that's what I meant earlier.  Perfect!
> 
> Nit:  I don't think vendor is the right term here.
> 
> Maybe something like:
> 
> iommut: split struct iommu_ops
> 
> Move the domain specific operations out of struct iommu_ops into a new
> structure that only has domain specific operations.  This solves
> the problem of needing to know if the method vector for a given
> operation needs to be retreived from the device or th domain.

Sure. Will use above description.

> 
>> +struct domain_ops {
> 
> This needs to keep an iommu in the name, i.e. iommu_domain_ops.

Sure.

> 
>> +	phys_addr_t (*iova_to_phys)(struct iommu_domain *domain, dma_addr_t iova);
> 
> Overly long line.

./scripts/checkpatch.pl --strict *.patch

didn't give me a WARN or CHECK. I will make it short anyway.

> 
>> +static inline void iommu_domain_set_ops(struct iommu_domain *domain,
>> +					const struct domain_ops *ops)
>> +{
>> +	domain->ops = ops;
>> +}
> 
> Do we really need this helper?

Unnecessary. I can set the pointer directly in the drivers.

> 
>> +static const struct domain_ops amd_domain_ops;
> 
> Can we avoid these forward declarations or would that cause too much
> churn?
> 

I don't like this either. But it's common to put the ops at the bottom
of the file in almost all iommu drivers.

Best regards,
baolu