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

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Message-ID: <20200220084552.GB11827@willie-the-truck>
Date:   Thu, 20 Feb 2020 08:45:52 +0000
From:   Will Deacon <will@...nel.org>
To:     isaacm@...eaurora.org
Cc:     Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@...radead.org>, pratikp@...eaurora.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 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?

Will