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

[Andrew Lunn <andrew@lunn.ch>]

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@redhat.com> wrote:
> 
> > On 11/15/24 17:31, Parker Newman wrote:
> > > From: Parker Newman <pnewman@connecttech.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