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

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Message-ID: <bb52bdc1-df2e-493d-a58f-df3143715150@lunn.ch>
Date: Sat, 16 Nov 2024 20:22:53 +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

On Fri, Nov 15, 2024 at 01:59:40PM -0500, Parker Newman wrote:
> On Fri, 15 Nov 2024 18:17:07 +0100
> Paolo Abeni <pabeni@...hat.com> wrote:
> 
> > On 11/15/24 17:31, Parker Newman wrote:
> > > From: Parker Newman <pnewman@...necttech.com>
> > >
> > > Read the iommu stream id from device tree rather than hard coding to mgbe0.
> > > Fixes kernel panics when using mgbe controllers other than mgbe0.
> >
> > It's better to include the full Oops backtrace, possibly decoded.
> >
> 
> Will do, there are many different ones but I can add the most common.
> 
> > > Tested with Orin AGX 64GB module on Connect Tech Forge carrier board.
> >
> > Since this looks like a fix, you should include a suitable 'Fixes' tag
> > here, and specify the 'net' target tree in the subj prefix.
> >
> 
> Sorry I missed the "net" tag.
> 
> The bug has existed since dwmac-tegra.c was added. I can add a Fixes tag but
> in the past I was told they aren't needed in that situation?
> 
> > > @@ -241,6 +243,12 @@ static int tegra_mgbe_probe(struct platform_device *pdev)
> > >  	if (IS_ERR(mgbe->xpcs))
> > >  		return PTR_ERR(mgbe->xpcs);
> > >
> > > +	/* get controller's stream id from iommu property in device tree */
> > > +	if (!tegra_dev_iommu_get_stream_id(mgbe->dev, &mgbe->iommu_sid)) {
> > > +		dev_err(mgbe->dev, "failed to get iommu stream id\n");
> > > +		return -EINVAL;
> > > +	}
> >
> > I *think* it would be better to fallback (possibly with a warning or
> > notice) to the previous default value when the device tree property is
> > not available, to avoid regressions.
> >
> 
> I debated this as well... In theory the iommu must be setup for the
> mgbe controller to work anyways. Doing it this way means the worst case is
> probe() fails and you lose an ethernet port.

New DT properties are always optional. Take the example of a board
only using a single controller. It should happily work. It probably
does not have this property because it is not needed. Your change is
likely to cause a regression on such a board.

Also, is a binding patch needed?

	Andrew