linux-kernel - Re: [PATCH 29/29] arm64: dts: qcom: Harmonize DWC USB3 DT nodes name

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Date:   Wed, 14 Jul 2021 15:48:07 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     John Stultz <john.stultz@...aro.org>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Felipe Balbi <balbi@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Amit Pundir <amit.pundir@...aro.org>
Subject: Re: [PATCH 29/29] arm64: dts: qcom: Harmonize DWC USB3 DT nodes name

Hello John,

On Tue, Jul 13, 2021 at 05:07:00PM -0700, John Stultz wrote:
> On Tue, Oct 20, 2020 at 5:10 AM Serge Semin
> <Sergey.Semin@...kalelectronics.ru> wrote:
> >
> > In accordance with the DWC USB3 bindings the corresponding node
> > name is suppose to comply with the Generic USB HCD DT schema, which
> > requires the USB nodes to have the name acceptable by the regexp:
> > "^usb(@.*)?" . Make sure the "snps,dwc3"-compatible nodes are correctly
> > named.
> >
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 

> I know folks like to ignore this, but this patch breaks AOSP on db845c. :(

Sorry to hear that. Alas there is no much can be done about it.
DT-nodes name is a subject of DT-schema convention and as we've finally
unified USB-controller nodes it shouldn't be reverted back. You can
find the final USB-controller bindings in:
Documentation/devicetree/bindings/usb/usb.yaml
It strictly defines to have USB-nodes with names like "usb(@.*)".
Reverting this patch will cause the DT-bindings check procedure
failure. You can also find the naming convention defined in the
latest DT spec:
https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.3

See also device-tree bindings requirements listed in the file:
Documentation/devicetree/bindings/writing-bindings.rst
It says: "DO use node names matching the class of the device. Many
standard names are defined in the DT Spec. If there isn't one,
consider adding it."

> 
> In the exact same way an earlier patch broke HiKey960:
>   https://lore.kernel.org/lkml/CALAqxLWGujgR7p8Vb5S_RimRVYxwm5XF-c4NkKgMH-43wEBaWg@mail.gmail.com/
> 
> (which I still have to carry a revert for).
> 
> I get that this change is useful so more dynamic userland can find
> devices using consistent naming with future kernels (but doesn't the
> dynamic userland have to handle the case for older kernels as well?)
> But for userland that uses static configs, its painful as updating
> userland to use the new node ids then causes older kernels to fail.
> 
> I'm looking into how we might be able to probe and set the property
> dynamically, but AOSP's init system is far more aligned to static
> configs.
> 

As Krzysztof said in
https://lore.kernel.org/lkml/20201221210423.GA2504@kozik-lap/
and Bjorn noted in his response to your email, the only way to solve
the problem is to fix the user-land app so one would be able to deal
with both old and new DT-nodes name. Alternatively you can just
replace the dts with older one, where the name still have
the "dwc3"-prefix.

-Sergey

> This will probably be ignored again, but it would be nice if we could
> have a release where DTS changes don't break userland for one of my
> boards. As it feels like its been awhile.
> 
> thanks
> -john