netdev - Re: [PATCH v1 1/1] net: stmmac: dwmac-tegra: Read iommu stream id from device tree

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Message-ID: <984a8471-7e49-4549-9d8a-48e1a29950f6@lunn.ch>
Date: Tue, 19 Nov 2024 01:50:18 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Parker Newman <parker@...est.io>
Cc: Paolo Abeni <pabeni@...hat.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Parker Newman <pnewman@...necttech.com>
Subject: Re: [PATCH v1 1/1] net: stmmac: dwmac-tegra: Read iommu stream id
 from device tree

> This is not a new dt property, the "iommus" property is an existing property
> that is parsed by the Nvidia implementation of the arm-smmu driver.
> 
> Here is a snippet from the device tree:
> 
> smmu_niso0: iommu@...00000 {
>         compatible = "nvidia,tegra234-smmu", "nvidia,smmu-500";
> ...
> }
> 
> /* MGBE0 */
> ethernet@...0000 {
> 	compatible = "nvidia,tegra234-mgbe";
> ...
> 	iommus = <&smmu_niso0 TEGRA234_SID_MGBE>;
> ...
> }
> 
> /* MGBE1 */
> ethernet@...0000 {
> 	compatible = "nvidia,tegra234-mgbe";
> ...
> 	iommus = <&smmu_niso0 TEGRA234_SID_MGBE_VF1>;
> ...
> }

What i was meaning does the nvidia,tegra234-mgbe binding allow iommus?
I just checked, yes it does.

> If the iommus property is missing completely from the MGBE's device tree node it
> causes secure read/write errors which spam the kernel log and can cause crashes.
> 
> I can add the fallback in V2 with a warning if that is preferred.

The fact it crashed makes me think it is optional. Any existing users
must work, otherwise it would crash, and then be debugged. I guess you
are pushing the usage further, and so have come across this condition.

Is the iommus a SoC property, or a board property? If it is a SoC
property, could you review all the SoC .dtsi files and fix up any
which are missing the property?

Adding a warning is O.K, but ideally the missing property should be
added first.

The merge window is open now, so patches will need to wait two weeks.

	Andrew