linux-kernel - Re: [RFC PATCH] arm64: dts: ls1028a: mark ARM SMMU as DMA coherent

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Message-ID: <20230105120447.vnr24pusr3ihdhwk@skbuf>
Date:   Thu, 5 Jan 2023 14:04:47 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     devicetree@...r.kernel.org, iommu@...ts.linux.dev,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-kernel@...r.kernel.org, Michael Walle <michael@...le.cc>
Subject: Re: [RFC PATCH] arm64: dts: ls1028a: mark ARM SMMU as DMA coherent

On Tue, Jan 03, 2023 at 06:12:29PM +0000, Robin Murphy wrote:
> > I have a side question, why is the dev_name() of your SMMU set to
> > "arm-smmu.0.auto" (determined by PLATFORM_DEVID_AUTO if I'm not mistaken)?
> 
> This is an ACPI-based machine, where platform device discovery and creation
> is... different :)
> 
> SMMUs are among those managed by drivers/acpi/arm64/iort.c
> 
> > I'm asking because I would like to study the mechanism through which
> > your SMMU platform device get probed, to make sure that it's not
> > possible, during shutdown, for both platform_driver :: shutdown()
> > and platform_driver :: remove() methods to get called by the driver core.
> > This is generally not disallowed, and even possible if the entity who
> > registers these platform devices has its ->shutdown() method pointing
> > at ->remove().
> 
> Yikes, I'd very much hope that that's not a thing!

Ah, ok. Appears to be fine. Looking at drivers/acpi/arm64/iort.c,
it seems that no one is removing those platform devices.