Re: [PATCH 3/3] arm64: tegra: Add iommu and dma properties for Tegra194 QSPI

[Aaron Kling]

On Wed, May 20, 2026 at 6:49 AM Thierry Reding <thierry.reding@xxxxxxxxx> wrote:
>
> On Fri, May 15, 2026 at 03:35:29PM -0500, Aaron Kling via B4 Relay wrote:
> > From: Aaron Kling <webgeek1234@xxxxxxxxx>
> >
> > Without iommu and dma enabled, flash storage such as the spi-nor on the
> > p3668 module times out and cannot complete any transfers.
> >
> > Signed-off-by: Aaron Kling <webgeek1234@xxxxxxxxx>
> > ---
> >  arch/arm64/boot/dts/nvidia/tegra194.dtsi | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/nvidia/tegra194.dtsi b/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> > index 1d659454a6f9fe..0e0a20befe9e68 100644
> > --- a/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> > +++ b/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> > @@ -923,6 +923,10 @@ spi@3270000 {
> >                                <&bpmp TEGRA194_CLK_QSPI0_PM>;
> >                       clock-names = "qspi", "qspi_out";
> >                       resets = <&bpmp TEGRA194_RESET_QSPI0>;
> > +                     iommus = <&smmu TEGRA194_SID_GPCDMA_0>;
> > +                     dma-coherent;
> > +                     dmas = <&gpcdma 5>, <&gpcdma 5>;
> > +                     dma-names = "rx", "tx";
>
> dmas and dma-names are the only properties that you should need here.

This is where I started and it didn't work. Without the iommu
properties, I get endless mmu faults upon accessing the qspi flash
device:

[   62.313833] tegra-mc 2c00000.memory-controller: axisw: secure write
@0x00000003ffffff00: VPR violation ((null))
[   62.324542] arm-smmu 12000000.iommu: Unhandled context fault:
fsr=0x402, iova=0xcd21d000, fsynr=0x80012, cbfrsynra=0x820, cb=1

I know downstream kernels aren't always (normally...) the arbiter of
sanity, but I did pull these from the Nvidia downstream 5.10 kernel,
which is where Nvidia was starting to try to align with mainline
paradigms. All of these properties are set there.

If the qspi node isn't supposed to set iommu directly, then there's a
larger problem here that I don't even know where to begin to look
into. All I can say is that dma fails with faults if they are not set
and works when they are.

Aaron