linux-kernel - Re: [PATCH 2/2] drivers/arm-smmu-v3: Implement .iotlb_sync

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Message-ID: <20250929124719.GJ2617119@nvidia.com>
Date: Mon, 29 Sep 2025 09:47:19 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: Daniel Mentz <danielmentz@...gle.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
	Pranjal Shrivastava <praan@...gle.com>,
	Liviu Dudau <liviu.dudau@....com>,
	Rob Clark <robin.clark@....qualcomm.com>
Subject: Re: [PATCH 2/2] drivers/arm-smmu-v3: Implement .iotlb_sync_map
 callback

On Mon, Sep 29, 2025 at 12:24:28PM +0000, Mostafa Saleh wrote:
> On Mon, Sep 29, 2025 at 08:58:03AM -0300, Jason Gunthorpe wrote:
> > On Sat, Sep 27, 2025 at 10:39:53PM +0000, Daniel Mentz wrote:
> > > @@ -3700,6 +3713,7 @@ static const struct iommu_ops arm_smmu_ops = {
> > >  		.map_pages		= arm_smmu_map_pages,
> > >  		.unmap_pages		= arm_smmu_unmap_pages,
> > >  		.flush_iotlb_all	= arm_smmu_flush_iotlb_all,
> > > +		.iotlb_sync_map		= arm_smmu_iotlb_sync_map,
> > 
> > Shouldn't this avoid defining the op on coherent systems?
> 
> Does that mean we need to have 2 iommu_ops, one for
> coherent/non-coherent SMMUs, as both can be mixed in the same system.

Yes, I think you'd have to do it with two ops..

It just seems wrong to penalize the normal fast case for these
systems.

Jason