linux-kernel - Re: [PATCH 0/2] iommu/arm-smmu: Add an optional "input-address-size" property

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Message-ID: <e99e07c2-88c6-e4d8-af80-c46d36bc6cd0@arm.com>
Date:   Fri, 11 Oct 2019 10:16:28 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Nicolin Chen <nicoleotsuka@...il.com>, joro@...tes.org,
        robh+dt@...nel.org, mark.rutland@....com, will@...nel.org
Cc:     vdumpa@...dia.com, iommu@...ts.linux-foundation.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/2] iommu/arm-smmu: Add an optional "input-address-size"
 property

On 2019-10-11 4:46 am, Nicolin Chen wrote:
> This series of patches add an optional DT property to allow an SoC to
> specify how many bits being physically connected to its SMMU instance,
> depending on the SoC design.

This has come up before, and it doesn't work in general because a single 
SMMU instance can have many master interfaces, with potentially 
different sizes of address bus wired up to each. It's also a 
conceptually-wrong approach anyway, since this isn't a property of the 
SMMU; it's a property of the interconnect(s) upstream of the SMMU.

IIRC you were working on Tegra - if so, Thierry already has a plan, see 
this thread: 
https://lore.kernel.org/linux-arm-kernel/20190930133510.GA1904140@ulmo/

Robin.

> 
> Nicolin Chen (2):
>    dt-bindings: arm-smmu: Add an optional "input-address-size" property
>    iommu/arm-smmu: Read optional "input-address-size" property
> 
>   Documentation/devicetree/bindings/iommu/arm,smmu.txt |  7 +++++++
>   drivers/iommu/arm-smmu.c                             | 10 ++++++++--
>   2 files changed, 15 insertions(+), 2 deletions(-)
>