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

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Date:   Tue, 13 Jul 2021 21:27:39 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        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>,
        "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>,
        Serge Semin <fancer.lancer@...il.com>,
        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

On Tue 13 Jul 19:07 CDT 2021, 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, I totally forgot that the name of that node is part of the USB
gadget configfs interface.

> 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.
> 

It won't help you, but having a mechanism to provide user friendly names
would certainly be welcome. I always struggle with the question of what
"6a00000.dwc3" (now .usb) actually is...

> 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.
> 
> 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.
> 

I don't have any preference to this being names "dwc3" or "usb" and we
could back out the change in time for v5.14. But you will still have the
problem for Hikey iiuc and the dts would then violate the binding - so
we need to fix that, and all the other Qualcomm boards defined by the
same binding.

Regards,
Bjorn