linux-kernel - Re: [RFC PATCH] iommu/dma: Allow drivers to reserve an iova range

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Date:   Thu, 20 Feb 2020 10:57:28 -0800
From:   Pratik Patel <pratikp@...eaurora.org>
To:     Will Deacon <will@...nel.org>
Cc:     isaacm@...eaurora.org, Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org, Liam Mark <lmark@...eaurora.org>,
        iommu@...ts.linux-foundation.org, kernel-team@...roid.com
Subject: Re: [RFC PATCH] iommu/dma: Allow drivers to reserve an iova range

On 02/20  08:45 am, Will Deacon wrote:
> On Wed, Feb 19, 2020 at 12:06:28PM -0800, isaacm@...eaurora.org wrote:
> > On 2020-02-19 03:15, Will Deacon wrote:
> > > On Tue, Feb 18, 2020 at 05:57:18PM -0800, isaacm@...eaurora.org wrote:
> > > > Does this mean that the driver should be managing the IOVA space and
> > > > mappings for this device using the IOMMU API? If so, is the
> > > > rationale for
> > > > this because the device driver can have the information of what IOVA
> > > > ranges
> > > > can and cannot be used? Shouldn't there be a generic way of
> > > > informing an
> > > > IOMMU driver about these reserved ranges? Perhaps through a device
> > > > tree
> > > > property, instead of deferring this type of management to the driver?
> > > 
> > > Before we dive into designing that, can you please clarify whether the
> > > reserved IOVA range applies to all DMA masters mastering through a
> > > particular SMMU, or whether it's just about one specific master? I was
> > > assuming the former, but wanted to be sure.
> > > 
> > This situation currently applies to one master.
> 
> Interesting. Is it problematic if the range is reserved for all masters
> sharing that SMMU?
> 
Yes, that would be an overkill. It certainly is useful and in
some cases quite helpful to not waste that range of IOVA space for
other masters on the same SMMU that can use it.

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