linux-kernel - Re: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved

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Message-ID: <20161114162037.GC14829@8bytes.org>
Date:   Mon, 14 Nov 2016 17:20:37 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     drjones@...hat.com, alex.williamson@...hat.com,
        jason@...edaemon.net, kvm@...r.kernel.org, marc.zyngier@....com,
        punit.agrawal@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, diana.craciun@....com,
        iommu@...ts.linux-foundation.org, pranav.sawargaonkar@...il.com,
        christoffer.dall@...aro.org, tglx@...utronix.de,
        robin.murphy@....com, linux-arm-kernel@...ts.infradead.org,
        eric.auger.pro@...il.com
Subject: Re: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved_regions
 callback

On Mon, Nov 14, 2016 at 05:08:16PM +0100, Auger Eric wrote:
> There are potentially several MSI doorbell physical pages in the SOC
> that are accessed through the IOMMU (translated). Each of those must
> have a corresponding IOVA and IOVA/PA mapping programmed in the IOMMU.
> Else MSI will fault.
> 
> - step 1 was to define a usable IOVA range for MSI mapping. So now we
> decided the base address and size would be hardcoded for ARM. The
> get_dm_region can be used to retrieve that hardcoded region.
> - Step2 is to allocate IOVAs within that range and map then for each of
> those MSI doorbells. This is done in the MSI controller compose() callback.
> 
> I hope I succeeded in clarifying this time.
> 
> Robin sent today a new version of its cookie think using a dummy
> allocator. I am currently integrating it.

Okay, I understand. A simple bitmap-allocator would probably be
sufficient, and doesn't have the overhead the iova allocator has. About
how many pages are we talking here?


	Joerg