linux-kernel - Re: [PATCH RFC 0/2] arm64: tegra: Add NVIDIA Jetson Nano 2GB Developer Kit support

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Message-ID: <CALHNRZ9Opg92SfMWHAJjDBwwnYG1BwW2qhscok=Sm+GacG1W9g@mail.gmail.com>
Date: Tue, 10 Jun 2025 14:45:53 -0500
From: Aaron Kling <webgeek1234@...il.com>
To: Thierry Reding <thierry.reding@...il.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Jonathan Hunter <jonathanh@...dia.com>, devicetree@...r.kernel.org, 
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/2] arm64: tegra: Add NVIDIA Jetson Nano 2GB
 Developer Kit support

On Tue, Jun 10, 2025 at 4:15 AM Thierry Reding <thierry.reding@...il.com> wrote:
>
> On Sun, Jun 08, 2025 at 11:25:53PM -0500, Aaron Kling wrote:
> > On Sun, Jun 8, 2025 at 11:24 PM Aaron Kling via B4 Relay
> > <devnull+webgeek1234.gmail.com@...nel.org> wrote:
> > >
> > > Signed-off-by: Aaron Kling <webgeek1234@...il.com>
> > > ---
> > > Aaron Kling (2):
> > >       dt-bindings: arm: tegra: Document Jetson Nano Devkits
> > >       arm64: tegra: Add NVIDIA Jetson Nano 2GB Developer Kit support
> > >
> > >  Documentation/devicetree/bindings/arm/tegra.yaml   |  5 +++
> > >  arch/arm64/boot/dts/nvidia/Makefile                |  2 +
> > >  arch/arm64/boot/dts/nvidia/tegra210-p3541-0000.dts | 43 ++++++++++++++++++++++
> > >  3 files changed, 50 insertions(+)
> > > ---
> > > base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
> > > change-id: 20250513-p3452-059708ca9993
> > >
> > > Best regards,
> > > --
> > > Aaron Kling <webgeek1234@...il.com>
> >
> > This is sent as an RFC, because it doesn't fully work. In my tests,
> > this boots and everything I can see works, except for hdmi. The
> > hotplug detect pin never changes, regardless of hdmi plug state. This
> > works as expected on the downstream 4.9 kernel. Based on the
> > downstream kernel dt for p3541, it's almost identical to p3540, and
> > I've mirrored those differences in this series. Things like the hpd
> > pin are the same. I'm failing to see why hpd would work on p3450, but
> > not on p3541, when using the same boot stack. Does anyone know why
> > this doesn't work?
>
> My recollection is that the HPD pin essentially loops back the +5V pin,
> so that would be my prime suspect. Other than that I suppose it could be
> a pinmux issue where HPD is muxed as something else.

This got me looking at which regulators got removed from the power
tree in my changes and it looks like the 3v3 usb hub one is the
operable difference. If I do the following in the new p3541 dts, hpd
works. This supply is not used downstream in p3541 for usb and is
instead replaced with a 5v0 regulator tied to gpio pi2. While looking
into this, I see that I got the usb power tree mapping wrong in v1 and
am fixing for v2.

+       /* This supply is associated with hdmi hotplug and needs to remain on */
+       regulator-vdd-hub-3v3 {
+               regulator-always-on;
+       };

This seems like a kludge, though. The implication is that whatever
gpio pa6 is wired to for p3541 is related to hpd somehow. I'm not sure
if the rail / wiring is different from p3450. Seems like it would have
to be. Any thoughts on this, Thierry? Maybe a better way to map the
dependency?

Sincerely,
Aaron