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

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Message-ID: <20241119131336.371af397.parker@finest.io>
Date: Tue, 19 Nov 2024 13:13:36 -0500
From: Parker Newman <parker@...est.io>
To: Andrew Lunn <andrew@...n.ch>
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

On Tue, 19 Nov 2024 01:50:18 +0100
Andrew Lunn <andrew@...n.ch> wrote:

> > 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.

I think there is some confusion here. I will try to summarize:
- Ihe iommu is supported by the Tegra SOC.
- The way the mgbe driver is written the iommu DT property is REQUIRED.
- "iommus" is a SOC DT property and is defined in tegra234.dtsi.
- The mgbe device tree nodes in tegra234.dtsi DO have the iommus property.
- There are no device tree changes required to to make this patch work.
- This patch works fine with existing device trees.

I will add the fallback however in case there is changes made to the iommu
subsystem in the future.

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

Ok thanks, I will wait a couple weeks to resend.
Parker