linux-kernel - RE: [PATCH] arm64: tegra: Enable hda node for P3737 + P3701

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Date:   Mon, 11 Apr 2022 09:56:50 +0000
From:   Mohan Kumar D <mkumard@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jonathan Hunter <jonathanh@...dia.com>
Subject: RE: [PATCH] arm64: tegra: Enable hda node for P3737 + P3701

Thierry,
Thanks for your explanation.

Krzysztof, 
Let me know if you still have any concern on the current patch.

-----Original Message-----
From: Thierry Reding <thierry.reding@...il.com> 
Sent: Wednesday, March 30, 2022 4:18 PM
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Mohan Kumar D <mkumard@...dia.com>; robh+dt@...nel.org; krzk+dt@...nel.org; devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; Jonathan Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH] arm64: tegra: Enable hda node for P3737 + P3701

On Fri, Mar 25, 2022 at 10:42:17AM +0100, Krzysztof Kozlowski wrote:
> On 25/03/2022 10:31, Mohan Kumar D wrote:
> > 
> > On 3/25/2022 12:56 PM, Krzysztof Kozlowski wrote:
> >> External email: Use caution opening links or attachments
> >>
> >>
> >> On 25/03/2022 08:21, Mohan Kumar wrote:
> >>> Add iommus property for hda and enable the node for P3737 + P3701 
> >>> platform.
> >>>
> >>> Signed-off-by: Mohan Kumar <mkumard@...dia.com>
> >>> ---
> >>>   arch/arm64/boot/dts/nvidia/tegra234-p3737-0000+p3701-0000.dts | 1 +
> >>>   arch/arm64/boot/dts/nvidia/tegra234.dtsi                      | 1 +
> >>>   2 files changed, 2 insertions(+)
> >>>
> >>> diff --git 
> >>> a/arch/arm64/boot/dts/nvidia/tegra234-p3737-0000+p3701-0000.dts 
> >>> b/arch/arm64/boot/dts/nvidia/tegra234-p3737-0000+p3701-0000.dts
> >>> index 34d6a01ee1c6..156d5d95fde7 100644
> >>> --- 
> >>> a/arch/arm64/boot/dts/nvidia/tegra234-p3737-0000+p3701-0000.dts
> >>> +++ b/arch/arm64/boot/dts/nvidia/tegra234-p3737-0000+p3701-0000.dt
> >>> +++ s
> >>> @@ -1751,6 +1751,7 @@
> >>>
> >>>                hda@...0000 {
> >>>                        nvidia,model = "NVIDIA Jetson AGX Orin 
> >>> HDA";
> >>> +                     status = "okay";
> >> Nodes are enabled by default. Why do you need this?
> > hda node status is set to "disabled" by default in soc dts file 
> > tegra234.dtsi. The enable is controlled by platform specific dts files.
> 
> Oh, surprise... why do you override nodes with full path? This is 
> error-prone and makes any changes (like node name fixing) difficult.
> This should be overridden by label.

I disagree, though I admit that this is probably very subjective. In my experience label references lead to completely unreadable DTS files.
We've had bad experiences with these kinds of references early on, so at some point we decided to discontinue that method on Tegra.

Reflecting the tree hierarchy in board-level DTS files on the other hand makes it very clear what you're changing and keeps the board-level DTS quite readable.

Fixing node names hasn't been a big problem for us and any potential remaining issues are entirely gone now that we can validate DTS files using dt-schema.

Thierry